aboutsummaryrefslogtreecommitdiff
path: root/doc/guix-cookbook.texi
blob: 2366c13caf8e18e8ce805a09f0bd39b9404d44ed (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
2466
2467
2468
2469
2470
2471
2472
2473
2474
2475
2476
2477
2478
2479
2480
2481
2482
2483
2484
2485
2486
2487
2488
2489
2490
2491
2492
2493
2494
2495
2496
2497
2498
2499
2500
2501
2502
2503
2504
2505
2506
2507
2508
2509
2510
2511
2512
2513
2514
2515
2516
2517
2518
2519
2520
2521
2522
2523
2524
2525
2526
2527
2528
2529
2530
2531
2532
2533
2534
2535
2536
2537
2538
2539
2540
2541
2542
2543
2544
2545
2546
2547
2548
2549
2550
2551
2552
2553
2554
2555
2556
2557
2558
2559
2560
2561
2562
2563
2564
2565
2566
2567
2568
2569
2570
2571
2572
2573
2574
2575
2576
2577
2578
2579
2580
2581
2582
2583
2584
2585
2586
2587
2588
2589
2590
2591
2592
2593
2594
2595
2596
2597
2598
2599
2600
2601
2602
2603
2604
2605
2606
2607
2608
2609
2610
2611
2612
2613
2614
2615
2616
2617
2618
2619
2620
2621
2622
2623
2624
2625
2626
2627
2628
2629
2630
2631
2632
2633
2634
2635
2636
2637
2638
2639
2640
2641
2642
2643
2644
2645
2646
2647
2648
2649
2650
2651
2652
2653
2654
2655
2656
2657
2658
2659
2660
2661
2662
2663
2664
2665
2666
2667
2668
2669
2670
2671
2672
2673
2674
2675
2676
2677
2678
2679
2680
2681
2682
2683
2684
2685
2686
2687
2688
2689
2690
2691
2692
2693
2694
2695
2696
2697
2698
2699
2700
2701
2702
2703
2704
2705
2706
2707
2708
2709
2710
2711
2712
2713
2714
2715
2716
2717
2718
2719
2720
2721
2722
2723
2724
2725
2726
2727
2728
2729
2730
2731
2732
2733
2734
2735
2736
2737
2738
2739
2740
2741
2742
2743
2744
2745
2746
2747
2748
2749
2750
2751
2752
2753
2754
2755
2756
2757
2758
2759
2760
2761
2762
2763
2764
2765
2766
2767
2768
2769
2770
2771
2772
2773
2774
2775
2776
2777
2778
2779
2780
2781
2782
2783
2784
2785
2786
2787
2788
2789
2790
2791
2792
2793
2794
2795
2796
2797
2798
2799
2800
2801
2802
2803
2804
2805
2806
2807
2808
2809
2810
2811
2812
2813
2814
2815
2816
2817
2818
2819
2820
2821
2822
2823
2824
2825
2826
2827
2828
2829
2830
2831
2832
2833
2834
2835
2836
2837
2838
2839
2840
2841
2842
2843
2844
2845
2846
2847
2848
2849
2850
2851
2852
2853
2854
2855
2856
2857
2858
2859
2860
2861
2862
2863
2864
2865
2866
2867
2868
2869
2870
2871
2872
2873
2874
2875
2876
2877
2878
2879
2880
2881
2882
2883
2884
2885
2886
2887
2888
2889
2890
2891
2892
2893
2894
2895
2896
2897
2898
2899
2900
2901
2902
2903
2904
2905
2906
2907
2908
2909
2910
2911
2912
2913
2914
2915
2916
2917
2918
2919
2920
2921
2922
2923
2924
2925
2926
2927
2928
2929
2930
2931
2932
2933
2934
2935
2936
2937
2938
2939
2940
2941
2942
2943
2944
2945
2946
2947
2948
2949
2950
2951
2952
2953
2954
2955
2956
2957
2958
2959
2960
2961
2962
2963
2964
2965
2966
2967
2968
2969
2970
2971
2972
2973
2974
2975
2976
2977
2978
2979
2980
2981
2982
2983
2984
2985
2986
2987
2988
2989
2990
2991
2992
2993
2994
2995
2996
2997
2998
2999
3000
3001
3002
3003
3004
3005
3006
3007
3008
3009
3010
3011
3012
3013
3014
3015
3016
3017
3018
3019
3020
3021
3022
3023
3024
3025
3026
3027
3028
3029
3030
3031
3032
3033
3034
3035
3036
3037
3038
3039
3040
3041
3042
3043
3044
3045
3046
3047
3048
3049
3050
3051
3052
3053
3054
3055
3056
3057
3058
3059
3060
3061
3062
3063
3064
3065
3066
3067
3068
3069
3070
3071
3072
3073
3074
3075
3076
3077
3078
3079
3080
3081
3082
3083
3084
3085
3086
3087
3088
3089
3090
3091
3092
3093
3094
3095
3096
3097
3098
3099
3100
3101
3102
3103
3104
3105
3106
3107
3108
3109
3110
3111
3112
3113
3114
3115
3116
3117
3118
3119
3120
3121
3122
3123
3124
3125
3126
3127
3128
3129
3130
3131
3132
3133
3134
3135
3136
3137
3138
3139
3140
3141
3142
3143
3144
3145
3146
3147
3148
3149
3150
3151
3152
3153
3154
3155
3156
3157
3158
3159
3160
3161
3162
3163
3164
3165
3166
3167
3168
3169
3170
3171
3172
3173
3174
3175
3176
3177
3178
3179
3180
3181
3182
3183
3184
3185
3186
3187
3188
3189
3190
3191
3192
3193
3194
3195
3196
3197
3198
3199
3200
3201
3202
3203
3204
3205
3206
3207
3208
3209
3210
3211
3212
3213
3214
3215
3216
3217
3218
3219
3220
3221
3222
3223
3224
3225
3226
3227
3228
3229
3230
3231
3232
3233
3234
3235
3236
3237
3238
3239
3240
3241
3242
3243
3244
3245
3246
3247
3248
3249
3250
3251
3252
3253
3254
3255
3256
3257
3258
3259
3260
3261
3262
3263
3264
3265
3266
3267
3268
3269
3270
3271
3272
3273
3274
3275
3276
3277
3278
3279
3280
3281
3282
3283
3284
3285
3286
3287
3288
3289
3290
3291
3292
3293
3294
3295
3296
3297
3298
3299
3300
3301
3302
3303
3304
3305
3306
3307
3308
3309
3310
3311
3312
3313
3314
3315
3316
3317
3318
3319
3320
3321
3322
3323
3324
3325
3326
3327
3328
3329
3330
3331
3332
3333
3334
3335
3336
3337
3338
3339
3340
3341
3342
3343
3344
3345
3346
3347
3348
3349
3350
3351
3352
3353
3354
3355
3356
3357
3358
3359
3360
3361
3362
3363
3364
3365
3366
3367
3368
3369
3370
3371
3372
3373
3374
3375
3376
3377
3378
3379
3380
3381
3382
3383
3384
3385
3386
3387
3388
3389
3390
3391
3392
3393
3394
3395
3396
3397
3398
3399
3400
3401
3402
3403
3404
3405
3406
3407
3408
3409
3410
3411
3412
3413
3414
3415
3416
3417
3418
3419
3420
3421
3422
3423
3424
3425
3426
3427
3428
3429
3430
3431
3432
3433
3434
3435
3436
3437
3438
3439
3440
3441
3442
3443
3444
3445
3446
3447
3448
3449
3450
3451
3452
3453
3454
3455
3456
3457
3458
3459
3460
3461
3462
3463
3464
3465
3466
3467
3468
3469
3470
3471
3472
3473
3474
3475
3476
3477
3478
3479
3480
3481
3482
3483
3484
3485
3486
3487
3488
3489
3490
3491
3492
3493
3494
3495
3496
3497
3498
3499
3500
3501
3502
3503
3504
3505
3506
3507
3508
3509
3510
3511
3512
3513
3514
3515
3516
3517
3518
3519
3520
3521
3522
3523
3524
3525
3526
3527
3528
3529
3530
3531
3532
3533
3534
3535
3536
3537
3538
3539
3540
3541
3542
3543
3544
3545
3546
3547
3548
3549
3550
3551
3552
3553
3554
3555
3556
3557
3558
3559
3560
3561
3562
3563
3564
3565
3566
3567
3568
3569
3570
3571
3572
3573
3574
3575
3576
3577
3578
3579
3580
3581
3582
3583
3584
3585
3586
3587
3588
3589
3590
3591
3592
3593
3594
3595
3596
3597
3598
3599
3600
3601
3602
3603
3604
3605
3606
3607
3608
3609
3610
3611
3612
3613
3614
3615
3616
3617
3618
3619
3620
3621
3622
3623
3624
3625
3626
3627
3628
3629
3630
3631
3632
3633
3634
3635
3636
3637
3638
3639
3640
3641
3642
3643
3644
3645
3646
3647
3648
3649
3650
3651
3652
3653
3654
3655
3656
3657
3658
3659
3660
3661
3662
3663
3664
3665
3666
3667
3668
3669
3670
3671
3672
3673
3674
3675
3676
3677
3678
3679
3680
3681
3682
3683
3684
3685
3686
3687
3688
3689
3690
3691
3692
3693
3694
3695
3696
3697
3698
3699
3700
3701
3702
3703
3704
3705
3706
3707
3708
3709
3710
3711
3712
3713
3714
3715
3716
3717
3718
3719
3720
3721
3722
3723
3724
3725
3726
3727
3728
3729
3730
3731
3732
3733
3734
3735
3736
3737
3738
3739
3740
3741
3742
3743
3744
3745
3746
3747
3748
3749
3750
3751
3752
3753
3754
3755
3756
3757
3758
3759
3760
3761
3762
3763
3764
3765
3766
3767
3768
3769
3770
3771
3772
3773
3774
3775
3776
3777
3778
3779
3780
3781
3782
3783
3784
3785
3786
3787
3788
3789
3790
3791
3792
3793
3794
3795
3796
3797
3798
3799
3800
3801
3802
3803
3804
3805
3806
3807
3808
3809
3810
3811
3812
3813
3814
3815
3816
3817
3818
3819
3820
3821
3822
3823
3824
3825
3826
3827
3828
3829
3830
3831
3832
3833
3834
3835
3836
3837
3838
3839
3840
3841
3842
3843
3844
3845
3846
3847
3848
3849
3850
3851
3852
3853
3854
3855
3856
3857
3858
3859
3860
3861
3862
3863
3864
3865
3866
3867
3868
3869
3870
3871
3872
3873
3874
3875
3876
3877
3878
3879
3880
3881
3882
3883
3884
3885
3886
3887
3888
3889
3890
3891
3892
3893
3894
3895
3896
3897
3898
3899
3900
3901
3902
3903
3904
3905
3906
3907
3908
3909
3910
3911
3912
3913
3914
3915
3916
3917
3918
3919
3920
3921
3922
3923
3924
3925
3926
3927
3928
3929
3930
3931
3932
3933
3934
3935
3936
3937
3938
3939
3940
3941
3942
3943
3944
3945
3946
3947
3948
3949
3950
3951
3952
3953
3954
3955
3956
3957
3958
3959
3960
3961
3962
3963
3964
3965
3966
3967
3968
3969
3970
3971
3972
3973
3974
3975
3976
3977
3978
3979
3980
3981
3982
3983
3984
3985
3986
3987
3988
3989
3990
3991
3992
3993
3994
3995
3996
3997
3998
3999
4000
4001
4002
4003
4004
4005
4006
4007
4008
4009
4010
4011
4012
4013
4014
4015
4016
4017
4018
4019
4020
4021
4022
4023
4024
4025
4026
4027
4028
4029
4030
4031
4032
4033
4034
4035
4036
4037
4038
4039
4040
4041
4042
4043
4044
4045
4046
4047
4048
4049
4050
4051
4052
4053
4054
4055
4056
4057
4058
4059
4060
4061
4062
4063
4064
4065
4066
4067
4068
4069
4070
4071
4072
4073
4074
4075
4076
4077
4078
4079
4080
4081
4082
4083
4084
4085
4086
4087
4088
4089
4090
4091
4092
4093
4094
4095
4096
4097
4098
4099
4100
4101
4102
4103
4104
4105
4106
4107
4108
4109
4110
4111
4112
4113
4114
4115
4116
4117
4118
4119
4120
4121
4122
4123
4124
4125
4126
4127
4128
4129
4130
4131
4132
4133
4134
4135
4136
4137
4138
4139
4140
4141
4142
4143
4144
4145
4146
4147
4148
4149
4150
4151
4152
4153
4154
4155
4156
4157
4158
4159
4160
4161
4162
4163
4164
4165
4166
4167
4168
4169
4170
4171
4172
4173
4174
4175
4176
4177
4178
4179
4180
4181
4182
4183
4184
4185
4186
4187
4188
4189
4190
4191
4192
4193
4194
4195
4196
4197
4198
4199
4200
4201
4202
4203
4204
4205
4206
4207
4208
4209
4210
4211
4212
4213
4214
4215
4216
4217
4218
4219
4220
4221
4222
4223
4224
4225
4226
4227
4228
4229
4230
4231
4232
4233
4234
4235
4236
4237
4238
4239
4240
4241
4242
4243
4244
4245
4246
4247
4248
4249
4250
4251
4252
4253
4254
4255
4256
4257
4258
4259
4260
4261
4262
4263
4264
4265
4266
4267
4268
4269
4270
4271
4272
4273
4274
4275
4276
4277
4278
4279
4280
4281
4282
4283
4284
4285
4286
4287
4288
4289
4290
4291
4292
4293
4294
4295
4296
4297
4298
4299
4300
4301
4302
4303
4304
4305
4306
4307
4308
4309
4310
4311
4312
4313
4314
4315
4316
4317
4318
4319
4320
4321
4322
4323
4324
4325
4326
4327
4328
4329
4330
4331
4332
4333
4334
4335
4336
4337
4338
4339
4340
4341
4342
4343
4344
4345
4346
4347
4348
4349
4350
4351
4352
4353
4354
4355
4356
4357
4358
4359
4360
4361
4362
4363
4364
4365
4366
4367
4368
4369
4370
4371
4372
4373
4374
4375
4376
4377
4378
4379
4380
4381
4382
4383
4384
4385
4386
4387
4388
4389
4390
4391
4392
4393
4394
4395
4396
4397
4398
4399
4400
4401
4402
4403
4404
4405
4406
4407
4408
4409
4410
4411
4412
4413
4414
4415
4416
4417
4418
4419
4420
4421
4422
4423
4424
4425
4426
4427
4428
4429
4430
4431
4432
4433
4434
4435
4436
4437
4438
4439
4440
4441
4442
4443
4444
4445
4446
4447
4448
4449
4450
4451
4452
4453
4454
4455
4456
4457
4458
4459
4460
4461
4462
4463
4464
4465
4466
4467
4468
4469
4470
4471
4472
4473
4474
4475
4476
4477
4478
4479
4480
4481
4482
4483
4484
4485
4486
4487
4488
4489
4490
4491
4492
4493
4494
4495
4496
4497
4498
4499
4500
4501
4502
4503
4504
4505
4506
4507
4508
4509
4510
4511
4512
4513
4514
4515
4516
4517
4518
4519
4520
4521
4522
4523
4524
4525
4526
4527
4528
4529
4530
4531
4532
4533
4534
4535
4536
4537
4538
4539
4540
4541
4542
4543
4544
4545
4546
4547
4548
4549
4550
4551
4552
4553
4554
4555
4556
4557
4558
4559
4560
4561
4562
4563
4564
4565
4566
4567
4568
4569
4570
4571
4572
4573
4574
4575
4576
4577
4578
4579
4580
4581
4582
4583
4584
4585
4586
4587
4588
4589
4590
4591
4592
4593
4594
4595
4596
4597
4598
4599
4600
4601
4602
4603
4604
4605
4606
4607
4608
4609
4610
4611
4612
4613
4614
4615
4616
4617
4618
4619
4620
4621
4622
4623
4624
4625
4626
4627
4628
4629
4630
4631
4632
4633
4634
4635
4636
4637
4638
4639
4640
4641
4642
4643
4644
4645
4646
4647
4648
4649
4650
4651
4652
4653
4654
4655
4656
4657
4658
4659
4660
4661
4662
4663
4664
4665
4666
4667
4668
4669
4670
4671
4672
4673
4674
4675
4676
4677
4678
4679
4680
4681
4682
4683
4684
4685
4686
4687
4688
4689
4690
4691
4692
4693
4694
4695
4696
4697
4698
4699
4700
4701
4702
4703
4704
4705
4706
4707
4708
4709
4710
4711
4712
4713
4714
4715
4716
4717
4718
4719
4720
4721
4722
4723
4724
4725
4726
4727
4728
4729
4730
4731
4732
4733
4734
4735
4736
4737
4738
4739
4740
4741
4742
4743
4744
4745
4746
4747
4748
4749
4750
4751
4752
4753
4754
4755
4756
4757
4758
4759
4760
4761
4762
4763
4764
4765
4766
4767
4768
4769
4770
4771
4772
4773
4774
4775
4776
4777
4778
4779
4780
4781
4782
4783
4784
4785
4786
4787
4788
4789
4790
4791
4792
4793
4794
4795
4796
4797
4798
4799
4800
4801
4802
4803
4804
4805
4806
4807
4808
4809
4810
4811
4812
4813
4814
4815
4816
4817
4818
4819
4820
4821
4822
4823
4824
4825
4826
4827
4828
4829
4830
4831
4832
4833
4834
4835
4836
4837
4838
4839
4840
4841
4842
4843
4844
4845
4846
4847
4848
4849
4850
4851
4852
4853
4854
4855
4856
4857
4858
4859
4860
4861
4862
4863
4864
4865
4866
4867
4868
4869
4870
4871
4872
4873
4874
4875
4876
4877
4878
4879
4880
4881
4882
4883
4884
4885
4886
4887
4888
4889
4890
4891
4892
4893
4894
4895
4896
4897
4898
4899
4900
4901
4902
4903
4904
4905
4906
4907
4908
4909
4910
4911
4912
4913
4914
4915
4916
4917
4918
4919
4920
4921
4922
4923
4924
4925
4926
4927
4928
4929
4930
4931
4932
4933
4934
4935
4936
4937
4938
4939
4940
4941
4942
4943
4944
4945
4946
4947
4948
4949
4950
4951
4952
4953
4954
4955
4956
4957
4958
4959
4960
4961
4962
4963
4964
4965
4966
4967
4968
4969
4970
4971
4972
4973
4974
4975
4976
4977
4978
4979
4980
4981
4982
4983
4984
4985
4986
4987
4988
4989
4990
4991
4992
4993
4994
4995
4996
4997
4998
4999
5000
5001
5002
5003
5004
5005
5006
5007
5008
5009
5010
5011
5012
5013
5014
5015
5016
5017
5018
5019
5020
5021
5022
5023
5024
5025
5026
5027
5028
5029
5030
5031
5032
5033
5034
5035
5036
5037
5038
5039
5040
5041
5042
5043
5044
5045
5046
5047
5048
5049
5050
5051
5052
5053
5054
5055
5056
5057
5058
5059
5060
5061
5062
5063
5064
5065
5066
5067
5068
5069
5070
5071
5072
5073
5074
5075
5076
5077
5078
5079
5080
5081
5082
5083
5084
5085
5086
5087
5088
5089
5090
5091
5092
5093
5094
5095
5096
5097
5098
5099
5100
5101
5102
5103
5104
5105
5106
5107
5108
5109
5110
5111
5112
5113
5114
5115
5116
5117
5118
5119
5120
5121
5122
5123
5124
5125
5126
5127
5128
5129
5130
5131
5132
5133
5134
5135
5136
5137
5138
5139
5140
5141
5142
5143
5144
5145
5146
5147
5148
5149
5150
5151
5152
5153
5154
5155
5156
5157
5158
5159
5160
5161
5162
5163
5164
5165
5166
5167
5168
5169
5170
5171
5172
5173
5174
5175
5176
5177
5178
5179
5180
5181
5182
5183
5184
5185
5186
5187
5188
5189
5190
5191
5192
5193
5194
5195
5196
5197
5198
5199
5200
5201
5202
5203
5204
5205
5206
5207
5208
5209
5210
5211
5212
5213
5214
5215
5216
5217
5218
5219
5220
5221
5222
5223
5224
5225
5226
5227
5228
5229
5230
5231
5232
5233
5234
5235
5236
5237
5238
5239
5240
5241
5242
5243
5244
5245
5246
5247
5248
5249
5250
5251
5252
5253
5254
5255
5256
5257
5258
5259
5260
5261
5262
5263
5264
5265
5266
5267
5268
5269
5270
5271
5272
5273
5274
5275
5276
5277
5278
5279
5280
5281
5282
5283
5284
5285
5286
5287
5288
5289
5290
5291
5292
5293
5294
5295
5296
5297
5298
5299
5300
5301
5302
5303
5304
5305
5306
5307
5308
5309
5310
5311
5312
5313
5314
5315
5316
5317
5318
5319
5320
5321
5322
5323
5324
5325
5326
5327
5328
5329
5330
5331
5332
5333
5334
5335
5336
5337
5338
5339
5340
5341
5342
5343
5344
5345
5346
5347
5348
5349
5350
5351
5352
5353
5354
5355
5356
5357
5358
5359
5360
5361
5362
5363
5364
5365
5366
5367
5368
5369
5370
5371
5372
5373
5374
5375
5376
5377
5378
5379
5380
5381
5382
5383
5384
5385
5386
5387
5388
5389
5390
5391
5392
5393
5394
5395
5396
5397
5398
5399
5400
5401
5402
5403
5404
5405
5406
5407
5408
5409
5410
5411
5412
5413
5414
5415
5416
5417
5418
5419
5420
5421
5422
5423
5424
5425
5426
5427
5428
5429
5430
5431
5432
5433
5434
5435
5436
5437
5438
5439
5440
5441
5442
5443
5444
5445
5446
5447
5448
5449
5450
5451
5452
5453
5454
5455
5456
5457
5458
5459
5460
5461
5462
5463
5464
5465
5466
5467
5468
5469
5470
5471
5472
5473
5474
5475
5476
5477
5478
5479
5480
5481
5482
5483
5484
5485
5486
5487
5488
5489
5490
5491
5492
5493
5494
5495
5496
5497
5498
5499
5500
5501
5502
5503
5504
5505
5506
5507
5508
5509
5510
5511
5512
5513
5514
5515
5516
5517
5518
5519
5520
5521
5522
5523
5524
5525
5526
5527
5528
5529
5530
5531
5532
5533
5534
\input texinfo
@c -*-texinfo-*-

@c %**start of header
@setfilename guix-cookbook.info
@documentencoding UTF-8
@settitle GNU Guix Cookbook
@c %**end of header

@c Onion service for ci.guix.gnu.org.
@set SUBSTITUTE-TOR-URL https://4zwzi66wwdaalbhgnix55ea3ab4pvvw66ll2ow53kjub6se4q2bclcyd.onion

@copying
Copyright @copyright{} 2019, 2022 Ricardo Wurmus@*
Copyright @copyright{} 2019 Efraim Flashner@*
Copyright @copyright{} 2019 Pierre Neidhardt@*
Copyright @copyright{} 2020 Oleg Pykhalov@*
Copyright @copyright{} 2020 Matthew Brooks@*
Copyright @copyright{} 2020 Marcin Karpezo@*
Copyright @copyright{} 2020 Brice Waegeneire@*
Copyright @copyright{} 2020 André Batista@*
Copyright @copyright{} 2020 Christine Lemmer-Webber@*
Copyright @copyright{} 2021 Joshua Branson@*
Copyright @copyright{} 2022, 2023 Maxim Cournoyer@*
Copyright @copyright{} 2023 Ludovic Courtès@*
Copyright @copyright{} 2023 Thomas Ieong

Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with no
Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.  A
copy of the license is included in the section entitled ``GNU Free
Documentation License''.
@end copying

@dircategory System administration
@direntry
* Guix cookbook: (guix-cookbook).    Tutorials and examples for GNU Guix.
@end direntry

@titlepage
@title GNU Guix Cookbook
@subtitle Tutorials and examples for using the GNU Guix Functional Package Manager
@author The GNU Guix Developers

@page
@vskip 0pt plus 1filll

@insertcopying
@end titlepage

@contents

@c *********************************************************************
@node Top
@top GNU Guix Cookbook

This document presents tutorials and detailed examples for GNU@tie{}Guix, a
functional package management tool written for the GNU system.  Please
@pxref{Top,,, guix, GNU Guix reference manual} for details about the system,
its API, and related concepts.

@c TRANSLATORS: You can replace the following paragraph with information on
@c how to join your own translation team and how to report issues with the
@c translation.
This manual is also available in French (@pxref{Top,,, guix-cookbook.fr,
Livre de recettes de GNU Guix}), German (@pxref{Top,,,
guix-cookbook.de, GNU-Guix-Kochbuch}) and Slovak (@pxref{Top,,,
guix-cookbook.sk, Receptár GNU Guix}).  If you would like to translate
this document in your native language, consider joining
@uref{https://translate.fedoraproject.org/projects/guix/documentation-cookbook,
Weblate} (@pxref{Translating Guix,,, guix, GNU Guix reference
manual}).

@menu
* Scheme tutorials::            Meet your new favorite language!
* Packaging::                   Packaging tutorials
* System Configuration::        Customizing the GNU System
* Containers::                  Isolated environments and nested systems
* Virtual Machines::            Virtual machines usage and configuration
* Advanced package management::  Power to the users!
* Software Development::        Environments, continuous integration, etc.
* Environment management::      Control environment
* Installing Guix on a Cluster::  High-performance computing.

* Acknowledgments::             Thanks!
* GNU Free Documentation License::  The license of this document.
* Concept Index::               Concepts.

@detailmenu
 --- The Detailed Node Listing ---

Scheme tutorials

* A Scheme Crash Course::

Packaging

* Packaging Tutorial::          A tutorial on how to add packages to Guix.

Packaging Tutorial

* A ``Hello World'' package::
* Setup::
* Extended example::
* Other build systems::
* Programmable and automated package definition::
* Getting help::
* Conclusion::
* References::

Setup

* Local file::
* Channels::
* Direct checkout hacking::

Programmable and automated package definition

* Recursive importers::
* Automatic update::
* Inheritance::

System Configuration

* Auto-Login to a Specific TTY::  Automatically Login a User to a Specific TTY
* Customizing the Kernel::      Creating and using a custom Linux kernel on Guix System.
* Guix System Image API::       Customizing images to target specific platforms.
* Using security keys::         How to use security keys with Guix System.
* Dynamic DNS mcron job::       Job to update the IP address behind a DuckDNS host name.
* Connecting to Wireguard VPN::  Connecting to a Wireguard VPN.
* Customizing a Window Manager::  Handle customization of a Window manager on Guix System.
* Running Guix on a Linode Server::  Running Guix on a Linode Server.
* Running Guix on a Kimsufi Server::  Running Guix on a Kimsufi Server.
* Setting up a bind mount::     Setting up a bind mount in the file-systems definition.
* Getting substitutes from Tor::  Configuring Guix daemon to get substitutes through Tor.
* Setting up NGINX with Lua::   Configuring NGINX web-server to load Lua modules.
* Music Server with Bluetooth Audio::  Headless music player with Bluetooth output.

Customizing a Window Manager

* StumpWM::
* Session lock::

Session lock

* Xorg::

Containers

* Guix Containers::             Perfectly isolated environments
* Guix System Containers::      A system inside your system

Guix System Containers

* A Database Container::
* Container Networking::

Virtual Machines

* Network bridge for QEMU::
* Routed network for libvirt::

Advanced package management

* Guix Profiles in Practice::   Strategies for multiple profiles and manifests.

Guix Profiles in Practice

* Basic setup with manifests::
* Required packages::
* Default profile::
* The benefits of manifests::
* Reproducible profiles::

Software Development

* Getting Started::             Step 0: using `guix shell'.
* Building with Guix::          Step 1: building your code.
* The Repository as a Channel::  Step 2: turning the repo in a channel.
* Package Variants::            Bonus: Defining variants.
* Setting Up Continuous Integration::  Step 3: continuous integration.
* Build Manifest::              Bonus: Manifest.
* Wrapping Up::                 Recap.

Environment management

* Guix environment via direnv::  Setup Guix environment with direnv

Installing Guix on a Cluster

* Setting Up a Head Node::      The node that runs the daemon.
* Setting Up Compute Nodes::    Client nodes.
* Cluster Network Access::      Dealing with network access restrictions.
* Cluster Disk Usage::          Disk usage considerations.
* Cluster Security Considerations::  Keeping the cluster secure.

@end detailmenu
@end menu

@c *********************************************************************
@node Scheme tutorials
@chapter Scheme tutorials

GNU@tie{}Guix is written in the general purpose programming language Scheme,
and many of its features can be accessed and manipulated programmatically.
You can use Scheme to generate package definitions, to modify them, to build
them, to deploy whole operating systems, etc.

Knowing the basics of how to program in Scheme will unlock many of the
advanced features Guix provides --- and you don't even need to be an
experienced programmer to use them!

Let's get started!

@menu
* A Scheme Crash Course::
@end menu

@node A Scheme Crash Course
@section A Scheme Crash Course

@cindex Scheme, crash course

Guix uses the Guile implementation of Scheme.  To start playing with the
language, install it with @code{guix install guile} and start a
@dfn{REPL}---short for @uref{https://en.wikipedia.org/wiki/Read%E2%80%93eval%E2%80%93print_loop,
@dfn{read-eval-print loop}}---by running @code{guile} from the command line.

Alternatively you can also run @code{guix shell guile -- guile}
if you'd rather not have Guile installed in your user profile.

In the following examples, lines show what you would type at the REPL;
lines starting with ``@result{}'' show evaluation results, while lines
starting with ``@print{}'' show things that get printed.  @xref{Using Guile
Interactively,,, guile, GNU Guile Reference Manual}, for more details on the
REPL.

@itemize
@item
Scheme syntax boils down to a tree of expressions (or @emph{s-expression} in
Lisp lingo).  An expression can be a literal such as numbers and strings, or a
compound which is a parenthesized list of compounds and literals.  @code{#true}
and @code{#false} (abbreviated @code{#t} and @code{#f}) stand for the
Booleans ``true'' and ``false'', respectively.

Examples of valid expressions:

@lisp
"Hello World!"
@result{} "Hello World!"

17
@result{} 17

(display (string-append "Hello " "Guix" "\n"))
@print{} Hello Guix!
@result{} #<unspecified>
@end lisp

@item
This last example is a function call nested in another function call.  When a
parenthesized expression is evaluated, the first term is the function and the
rest are the arguments passed to the function.  Every function returns the
last evaluated expression as its return value.

@item
Anonymous functions---@dfn{procedures} in Scheme parlance---are declared
with the @code{lambda} term:

@lisp
(lambda (x) (* x x))
@result{} #<procedure 120e348 at <unknown port>:24:0 (x)>
@end lisp

The above procedure returns the square of its argument.  Since everything is
an expression, the @code{lambda} expression returns an anonymous procedure,
which can in turn be applied to an argument:

@lisp
((lambda (x) (* x x)) 3)
@result{} 9
@end lisp

Procedures are regular values just like numbers, strings, Booleans, and
so on.

@item
Anything can be assigned a global name with @code{define}:

@lisp
(define a 3)
(define square (lambda (x) (* x x)))
(square a)
@result{} 9
@end lisp

@item
Procedures can be defined more concisely with the following syntax:

@lisp
(define (square x) (* x x))
@end lisp

@item
A list structure can be created with the @code{list} procedure:

@lisp
(list 2 a 5 7)
@result{} (2 3 5 7)
@end lisp

@item
Standard procedures are provided by the @code{(srfi srfi-1)} module to
create and process lists (@pxref{SRFI-1, list processing,, guile, GNU
Guile Reference Manual}).  Here are some of the most useful ones in
action:

@lisp
(use-modules (srfi srfi-1))  ;import list processing procedures

(append (list 1 2) (list 3 4))
@result{} (1 2 3 4)

(map (lambda (x) (* x x)) (list 1 2 3 4))
@result{} (1 4 9 16)

(delete 3 (list 1 2 3 4))        @result{} (1 2 4)
(filter odd? (list 1 2 3 4))     @result{} (1 3)
(remove even? (list 1 2 3 4))    @result{} (1 3)
(find number? (list "a" 42 "b")) @result{} 42
@end lisp

Notice how the first argument to @code{map}, @code{filter},
@code{remove}, and @code{find} is a procedure!

@item
@cindex S-expression
The @dfn{quote} disables evaluation of a parenthesized expression, also
called an S-expression or ``s-exp'': the first term is not called over
the other terms (@pxref{Expression Syntax, quote,, guile, GNU Guile
Reference Manual}).  Thus it effectively returns a list of terms.

@lisp
'(display (string-append "Hello " "Guix" "\n"))
@result{} (display (string-append "Hello " "Guix" "\n"))

'(2 a 5 7)
@result{} (2 a 5 7)
@end lisp

@item
The @code{quasiquote} (@code{`}, a backquote) disables evaluation of a
parenthesized expression until @code{unquote} (@code{,}, a comma)
re-enables it.  Thus it provides us with fine-grained control over what
is evaluated and what is not.

@lisp
`(2 a 5 7 (2 ,a 5 ,(+ a 4)))
@result{} (2 a 5 7 (2 3 5 7))
@end lisp

Note that the above result is a list of mixed elements: numbers, symbols (here
@code{a}) and the last element is a list itself.

@item
@cindex G-expressions, syntax
@cindex gexps, syntax
@findex #~
@findex #$
@findex gexp
@findex ungexp
Guix defines a variant of S-expressions on steroids called
@dfn{G-expressions} or ``gexps'', which come with a variant of
@code{quasiquote} and @code{unquote}: @code{#~} (or @code{gexp}) and
@code{#$} (or @code{ungexp}).  They let you @emph{stage code for later
execution}.

For example, you'll encounter gexps in some package definitions where
they provide code to be executed during the package build process.  They
look like this:

@lisp
(use-modules (guix gexp)           ;so we can write gexps
             (gnu packages base))  ;for 'coreutils'

;; Below is a G-expression representing staged code.
#~(begin
    ;; Invoke 'ls' from the package defined by the 'coreutils'
    ;; variable.
    (system* #$(file-append coreutils "/bin/ls") "-l")

    ;; Create this package's output directory.
    (mkdir #$output))
@end lisp

@xref{G-Expressions,,, guix, GNU Guix Reference Manual}, for more on
gexps.

@item
Multiple variables can be named locally with @code{let} (@pxref{Local
Bindings,,, guile, GNU Guile Reference Manual}):

@lisp
(define x 10)
(let ((x 2)
      (y 3))
  (list x y))
@result{} (2 3)

x
@result{} 10

y
@error{} In procedure module-lookup: Unbound variable: y
@end lisp

Use @code{let*} to allow later variable declarations to refer to earlier
definitions.

@lisp
(let* ((x 2)
       (y (* x 3)))
  (list x y))
@result{} (2 6)
@end lisp

@item
@dfn{Keywords} are typically used to identify the named parameters of a
procedure.  They are prefixed by @code{#:} (hash, colon) followed by
alphanumeric characters: @code{#:like-this}.
@xref{Keywords,,, guile, GNU Guile Reference Manual}.

@item
The percentage @code{%} is typically used for read-only global variables in
the build stage.  Note that it is merely a convention, like @code{_} in C.
Scheme treats @code{%} exactly the same as any other letter.

@item
Modules are created with @code{define-module} (@pxref{Creating Guile
Modules,,, guile, GNU Guile Reference Manual}).  For instance

@lisp
(define-module (guix build-system ruby)
  #:use-module (guix store)
  #:export (ruby-build
            ruby-build-system))
@end lisp

defines the module @code{guix build-system ruby} which must be located in
@file{guix/build-system/ruby.scm} somewhere in the Guile load path.  It
depends on the @code{(guix store)} module and it exports two variables,
@code{ruby-build} and @code{ruby-build-system}.

@xref{Package Modules,,, guix, GNU Guix Reference Manual}, for info on
modules that define packages.
@end itemize

@quotation Going further
Scheme is a language that has been widely used to teach programming and
you'll find plenty of material using it as a vehicle.  Here's a
selection of documents to learn more about Scheme:

@itemize
@item
@uref{https://spritely.institute/static/papers/scheme-primer.html, @i{A
Scheme Primer}}, by Christine Lemmer-Webber and the Spritely Institute.

@item
@uref{http://www.troubleshooters.com/codecorn/scheme_guile/hello.htm,
@i{Scheme at a Glance}}, by Steve Litt.

@item
@c There used to be a copy at mitpress.mit.edu but it vanished.
@uref{https://sarabander.github.io/sicp/,
@i{Structure and Interpretation of Computer Programs}}, by Harold
Abelson and Gerald Jay Sussman, with Julie Sussman.  Colloquially known
as ``SICP'', this book is a reference.

You can also install it and read it from your computer:

@example
guix install sicp info-reader
info sicp
@end example

@end itemize

You'll find more books, tutorials and other resources at
@url{https://schemers.org/}.
@end quotation


@c *********************************************************************
@node Packaging
@chapter Packaging

@cindex packaging

This chapter is dedicated to teaching you how to add packages to the
collection of packages that come with GNU Guix.  This involves writing package
definitions in Guile Scheme, organizing them in package modules, and building
them.

@menu
* Packaging Tutorial::          A tutorial on how to add packages to Guix.
@end menu

@node Packaging Tutorial
@section Packaging Tutorial

GNU Guix stands out as the @emph{hackable} package manager, mostly because it
uses @uref{https://www.gnu.org/software/guile/, GNU Guile}, a powerful
high-level programming language, one of the
@uref{https://en.wikipedia.org/wiki/Scheme_%28programming_language%29, Scheme}
dialects from the
@uref{https://en.wikipedia.org/wiki/Lisp_%28programming_language%29, Lisp family}.

Package definitions are also written in Scheme, which empowers Guix in some
very unique ways, unlike most other package managers that use shell scripts or
simple languages.

@itemize
@item
Use functions, structures, macros and all of Scheme expressiveness for your
package definitions.

@item
Inheritance makes it easy to customize a package by inheriting from it and
modifying only what is needed.

@item
Batch processing: the whole package collection can be parsed, filtered and
processed.  Building a headless server with all graphical interfaces stripped
out?  It's possible.  Want to rebuild everything from source using specific
compiler optimization flags?  Pass the @code{#:make-flags "..."} argument to
the list of packages.  It wouldn't be a stretch to think
@uref{https://wiki.gentoo.org/wiki/USE_flag, Gentoo USE flags} here, but this
goes even further: the changes don't have to be thought out beforehand by the
packager, they can be @emph{programmed} by the user!
@end itemize

The following tutorial covers all the basics around package creation with Guix.
It does not assume much knowledge of the Guix system nor of the Lisp language.
The reader is only expected to be familiar with the command line and to have some
basic programming knowledge.

@menu
* A ``Hello World'' package::
* Setup::
* Extended example::
* Other build systems::
* Programmable and automated package definition::
* Getting help::
* Conclusion::
* References::
@end menu

@node A ``Hello World'' package
@subsection A ``Hello World'' package

The ``Defining Packages'' section of the manual introduces the basics of Guix
packaging (@pxref{Defining Packages,,, guix, GNU Guix Reference Manual}).  In
the following section, we will partly go over those basics again.

GNU@tie{}Hello is a dummy project that serves as an idiomatic example for
packaging.  It uses the GNU build system (@code{./configure && make && make
install}).  Guix already provides a package definition which is a perfect
example to start with.  You can look up its declaration with @code{guix edit
hello} from the command line.  Let's see how it looks:

@lisp
(define-public hello
  (package
    (name "hello")
    (version "2.10")
    (source (origin
              (method url-fetch)
              (uri (string-append "mirror://gnu/hello/hello-" version
                                  ".tar.gz"))
              (sha256
               (base32
                "0ssi1wpaf7plaswqqjwigppsg5fyh99vdlb9kzl7c9lng89ndq1i"))))
    (build-system gnu-build-system)
    (synopsis "Hello, GNU world: An example GNU package")
    (description
     "GNU Hello prints the message \"Hello, world!\" and then exits.  It
serves as an example of standard GNU coding practices.  As such, it supports
command-line arguments, multiple languages, and so on.")
    (home-page "https://www.gnu.org/software/hello/")
    (license gpl3+)))
@end lisp

As you can see, most of it is rather straightforward.  But let's review the
fields together:

@table @samp
@item name
The project name.  Using Scheme conventions, we prefer to keep it
lower case, without underscore and using dash-separated words.

@item source
This field contains a description of the source code origin.  The
@code{origin} record contains these fields:

@enumerate
@item  The method, here @code{url-fetch} to download via HTTP/FTP, but other methods
    exist, such as @code{git-fetch} for Git repositories.
@item  The URI, which is typically some @code{https://} location for @code{url-fetch}.  Here
    the special `mirror://gnu` refers to a set of well known locations, all of
    which can be used by Guix to fetch the source, should some of them fail.
@item  The @code{sha256} checksum of the requested file.  This is essential to ensure
    the source is not corrupted.  Note that Guix works with base32 strings,
    hence the call to the @code{base32} function.
@end enumerate

@item build-system

This is where the power of abstraction provided by the Scheme language really
shines: in this case, the @code{gnu-build-system} abstracts away the famous
@code{./configure && make && make install} shell invocations.  Other build
systems include the @code{trivial-build-system} which does not do anything and
requires from the packager to program all the build steps, the
@code{python-build-system}, the @code{emacs-build-system}, and many more
(@pxref{Build Systems,,, guix, GNU Guix Reference Manual}).

@item synopsis
It should be a concise summary of what the package does.  For many packages a
tagline from the project's home page can be used as the synopsis.

@item description
Same as for the synopsis, it's fine to re-use the project description from the
homepage.  Note that Guix uses Texinfo syntax.

@item home-page
Use HTTPS if available.

@item license
See @code{guix/licenses.scm} in the project source for a full list of
available licenses.
@end table

Time to build our first package!  Nothing fancy here for now: we will stick to a
dummy @code{my-hello}, a copy of the above declaration.

As with the ritualistic ``Hello World'' taught with most programming languages,
this will possibly be the most ``manual'' approach.  We will work out an ideal
setup later; for now we will go the simplest route.

Save the following to a file @file{my-hello.scm}.

@lisp
(use-modules (guix packages)
             (guix download)
             (guix build-system gnu)
             (guix licenses))

(package
  (name "my-hello")
  (version "2.10")
  (source (origin
            (method url-fetch)
            (uri (string-append "mirror://gnu/hello/hello-" version
                                ".tar.gz"))
            (sha256
             (base32
              "0ssi1wpaf7plaswqqjwigppsg5fyh99vdlb9kzl7c9lng89ndq1i"))))
  (build-system gnu-build-system)
  (synopsis "Hello, Guix world: An example custom Guix package")
  (description
   "GNU Hello prints the message \"Hello, world!\" and then exits.  It
serves as an example of standard GNU coding practices.  As such, it supports
command-line arguments, multiple languages, and so on.")
  (home-page "https://www.gnu.org/software/hello/")
  (license gpl3+))
@end lisp

We will explain the extra code in a moment.

Feel free to play with the different values of the various fields.  If you
change the source, you'll need to update the checksum.  Indeed, Guix refuses to
build anything if the given checksum does not match the computed checksum of the
source code.  To obtain the correct checksum of the package declaration, we
need to download the source, compute the sha256 checksum and convert it to
base32.

Thankfully, Guix can automate this task for us; all we need is to provide the
URI:

@c TRANSLATORS: This is example shell output.
@example sh
$ guix download mirror://gnu/hello/hello-2.10.tar.gz

Starting download of /tmp/guix-file.JLYgL7
From https://ftpmirror.gnu.org/gnu/hello/hello-2.10.tar.gz...
following redirection to `https://mirror.ibcp.fr/pub/gnu/hello/hello-2.10.tar.gz'...
 …10.tar.gz  709KiB                                 2.5MiB/s 00:00 [##################] 100.0%
/gnu/store/hbdalsf5lpf01x4dcknwx6xbn6n5km6k-hello-2.10.tar.gz
0ssi1wpaf7plaswqqjwigppsg5fyh99vdlb9kzl7c9lng89ndq1i
@end example

In this specific case the output tells us which mirror was chosen.
If the result of the above command is not the same as in the above snippet,
update your @code{my-hello} declaration accordingly.

Note that GNU package tarballs come with an OpenPGP signature, so you
should definitely check the signature of this tarball with `gpg` to
authenticate it before going further:

@c TRANSLATORS: This is example shell output.
@example sh
$ guix download mirror://gnu/hello/hello-2.10.tar.gz.sig

Starting download of /tmp/guix-file.03tFfb
From https://ftpmirror.gnu.org/gnu/hello/hello-2.10.tar.gz.sig...
following redirection to `https://ftp.igh.cnrs.fr/pub/gnu/hello/hello-2.10.tar.gz.sig'...
 ….tar.gz.sig  819B                                                                                                                       1.2MiB/s 00:00 [##################] 100.0%
/gnu/store/rzs8wba9ka7grrmgcpfyxvs58mly0sx6-hello-2.10.tar.gz.sig
0q0v86n3y38z17rl146gdakw9xc4mcscpk8dscs412j22glrv9jf
$ gpg --verify /gnu/store/rzs8wba9ka7grrmgcpfyxvs58mly0sx6-hello-2.10.tar.gz.sig /gnu/store/hbdalsf5lpf01x4dcknwx6xbn6n5km6k-hello-2.10.tar.gz
gpg: Signature made Sun 16 Nov 2014 01:08:37 PM CET
gpg:                using RSA key A9553245FDE9B739
gpg: Good signature from "Sami Kerola <kerolasa@@iki.fi>" [unknown]
gpg:                 aka "Sami Kerola (http://www.iki.fi/kerolasa/) <kerolasa@@iki.fi>" [unknown]
gpg: WARNING: This key is not certified with a trusted signature!
gpg:          There is no indication that the signature belongs to the owner.
Primary key fingerprint: 8ED3 96E3 7E38 D471 A005  30D3 A955 3245 FDE9 B739
@end example

You can then happily run

@c TRANSLATORS: Do not translate this command
@example sh
$ guix package --install-from-file=my-hello.scm
@end example

You should now have @code{my-hello} in your profile!

@c TRANSLATORS: Do not translate this command
@example sh
$ guix package --list-installed=my-hello
my-hello	2.10	out
/gnu/store/f1db2mfm8syb8qvc357c53slbvf1g9m9-my-hello-2.10
@end example

We've gone as far as we could without any knowledge of Scheme.  Before moving
on to more complex packages, now is the right time to brush up on your Scheme
knowledge.  @pxref{A Scheme Crash Course} to get up to speed.

@node Setup
@subsection Setup

In the rest of this chapter we will rely on some basic Scheme
programming knowledge.  Now let's detail the different possible setups
for working on Guix packages.

There are several ways to set up a Guix packaging environment.

We recommend you work directly on the Guix source checkout since it makes it
easier for everyone to contribute to the project.

But first, let's look at other possibilities.

@menu
* Local file::
* Channels::
* Direct checkout hacking::
@end menu

@node Local file
@subsubsection Local file

This is what we previously did with @samp{my-hello}.  With the Scheme basics we've
covered, we are now able to explain the leading chunks.  As stated in @code{guix
package --help}:

@example
  -f, --install-from-file=FILE
                         install the package that the code within FILE
                         evaluates to
@end example

Thus the last expression @emph{must} return a package, which is the case in our
earlier example.

The @code{use-modules} expression tells which of the modules we need in the file.
Modules are a collection of values and procedures.  They are commonly called
``libraries'' or ``packages'' in other programming languages.

@node Channels
@subsubsection Channels

@cindex channel
Guix and its package collection can be extended through @dfn{channels}.
A channel is a Git repository, public or not, containing @file{.scm}
files that provide packages (@pxref{Defining Packages,,, guix, GNU Guix
Reference Manual}) or services (@pxref{Defining Services,,, guix, GNU
Guix Reference Manual}).

How would you go about creating a channel?  First, create a directory
that will contain your @file{.scm} files, say @file{~/my-channel}:

@example
mkdir ~/my-channel
@end example

Suppose you want to add the @samp{my-hello} package we saw previously;
it first needs some adjustments:

@lisp
(define-module (my-hello)
  #:use-module (guix licenses)
  #:use-module (guix packages)
  #:use-module (guix build-system gnu)
  #:use-module (guix download))

(define-public my-hello
  (package
    (name "my-hello")
    (version "2.10")
    (source (origin
              (method url-fetch)
              (uri (string-append "mirror://gnu/hello/hello-" version
                                  ".tar.gz"))
              (sha256
               (base32
                "0ssi1wpaf7plaswqqjwigppsg5fyh99vdlb9kzl7c9lng89ndq1i"))))
    (build-system gnu-build-system)
    (synopsis "Hello, Guix world: An example custom Guix package")
    (description
     "GNU Hello prints the message \"Hello, world!\" and then exits.  It
serves as an example of standard GNU coding practices.  As such, it supports
command-line arguments, multiple languages, and so on.")
    (home-page "https://www.gnu.org/software/hello/")
    (license gpl3+)))
@end lisp

Note that we have assigned the package value to an exported variable name with
@code{define-public}.  This is effectively assigning the package to the @code{my-hello}
variable so that it can be referenced, among other as dependency of other
packages.

If you use @code{guix package --install-from-file=my-hello.scm} on the above file, it
will fail because the last expression, @code{define-public}, does not return a
package.  If you want to use @code{define-public} in this use-case nonetheless, make
sure the file ends with an evaluation of @code{my-hello}:

@lisp
;; ...
(define-public my-hello
  ;; ...
  )

my-hello
@end lisp

This last example is not very typical.

Now how do you make that package visible to @command{guix} commands so
you can test your packages?  You need to add the directory to the search
path using the @option{-L} command-line option, as in these examples:

@example
guix show -L ~/my-channel my-hello
guix build -L ~/my-channel my-hello
@end example

The final step is to turn @file{~/my-channel} into an actual channel,
making your package collection seamlessly available @i{via} any
@command{guix} command.  To do that, you first need to make it a Git
repository:

@example
cd ~/my-channel
git init
git add my-hello.scm
git commit -m "First commit of my channel."
@end example

And that's it, you have a channel!  From there on, you can add this
channel to your channel configuration in
@file{~/.config/guix/channels.scm} (@pxref{Specifying Additional
Channels,,, guix, GNU Guix Reference Manual}); assuming you keep your
channel local for now, the @file{channels.scm} would look something like
this:

@lisp
(append (list (channel
                (name 'my-channel)
                (url (string-append "file://" (getenv "HOME")
                                    "/my-channel"))))
        %default-channels)
@end lisp

Next time you run @command{guix pull}, your channel will be picked up
and the packages it defines will be readily available to all the
@command{guix} commands, even if you do not pass @option{-L}.  The
@command{guix describe} command will show that Guix is, indeed, using
both the @code{my-channel} and the @code{guix} channels.

@xref{Creating a Channel,,, guix, GNU Guix Reference Manual}, for
details.

@node Direct checkout hacking
@subsubsection Direct checkout hacking

Working directly on the Guix project is recommended: it reduces the friction
when the time comes to submit your changes upstream to let the community benefit
from your hard work!

Unlike most software distributions, the Guix repository holds in one place both
the tooling (including the package manager) and the package definitions.  This
choice was made so that it would give developers the flexibility to modify the
API without breakage by updating all packages at the same time.  This reduces
development inertia.

Check out the official @uref{https://git-scm.com/, Git} repository:

@example
$ git clone https://git.savannah.gnu.org/git/guix.git
@end example

In the rest of this article, we use @samp{$GUIX_CHECKOUT} to refer to the location of
the checkout.


Follow the instructions in the manual (@pxref{Contributing,,, guix, GNU Guix
Reference Manual}) to set up the repository environment.

Once ready, you should be able to use the package definitions from the
repository environment.

Feel free to edit package definitions found in @samp{$GUIX_CHECKOUT/gnu/packages}.

The @samp{$GUIX_CHECKOUT/pre-inst-env} script lets you use @samp{guix} over the package
collection of the repository (@pxref{Running Guix Before It Is
Installed,,, guix, GNU Guix Reference Manual}).

@itemize
@item
Search packages, such as Ruby:

@example
  $ cd $GUIX_CHECKOUT
  $ ./pre-inst-env guix package --list-available=ruby
      ruby    1.8.7-p374      out     gnu/packages/ruby.scm:119:2
      ruby    2.1.6   out     gnu/packages/ruby.scm:91:2
      ruby    2.2.2   out     gnu/packages/ruby.scm:39:2
@end example

@item
Build a package, here Ruby version 2.1:

@example
  $ ./pre-inst-env guix build --keep-failed ruby@@2.1
  /gnu/store/c13v73jxmj2nir2xjqaz5259zywsa9zi-ruby-2.1.6
@end example

@item
Install it to your user profile:

@example
  $ ./pre-inst-env guix package --install ruby@@2.1
@end example

@item
Check for common mistakes:

@example
  $ ./pre-inst-env guix lint ruby@@2.1
@end example
@end itemize

Guix strives at maintaining a high packaging standard; when contributing to the
Guix project, remember to

@itemize
@item
follow the coding style (@pxref{Coding Style,,, guix, GNU Guix Reference Manual}),
@item
and review the check list from the manual (@pxref{Submitting Patches,,, guix, GNU Guix Reference Manual}).
@end itemize

Once you are happy with the result, you are welcome to send your contribution to
make it part of Guix.  This process is also detailed in the manual.  (@pxref{Contributing,,, guix, GNU Guix Reference Manual})


It's a community effort so the more join in, the better Guix becomes!

@node Extended example
@subsection Extended example

The above ``Hello World'' example is as simple as it goes.  Packages can be more
complex than that and Guix can handle more advanced scenarios.  Let's look at
another, more sophisticated package (slightly modified from the source):

@lisp
(define-module (gnu packages version-control)
  #:use-module ((guix licenses) #:prefix license:)
  #:use-module (guix utils)
  #:use-module (guix packages)
  #:use-module (guix git-download)
  #:use-module (guix build-system cmake)
  #:use-module (gnu packages compression)
  #:use-module (gnu packages pkg-config)
  #:use-module (gnu packages python)
  #:use-module (gnu packages ssh)
  #:use-module (gnu packages tls)
  #:use-module (gnu packages web))

(define-public my-libgit2
  (let ((commit "e98d0a37c93574d2c6107bf7f31140b548c6a7bf")
        (revision "1"))
    (package
      (name "my-libgit2")
      (version (git-version "0.26.6" revision commit))
      (source (origin
                (method git-fetch)
                (uri (git-reference
                      (url "https://github.com/libgit2/libgit2/")
                      (commit commit)))
                (file-name (git-file-name name version))
                (sha256
                 (base32
                  "17pjvprmdrx4h6bb1hhc98w9qi6ki7yl57f090n9kbhswxqfs7s3"))
                (patches (search-patches "libgit2-mtime-0.patch"))
                (modules '((guix build utils)))
                ;; Remove bundled software.
                (snippet '(delete-file-recursively "deps"))))
      (build-system cmake-build-system)
      (outputs '("out" "debug"))
      (arguments
       `(#:tests? #true                         ; Run the test suite (this is the default)
         #:configure-flags '("-DUSE_SHA1DC=ON") ; SHA-1 collision detection
         #:phases
         (modify-phases %standard-phases
           (add-after 'unpack 'fix-hardcoded-paths
             (lambda _
               (substitute* "tests/repo/init.c"
                 (("#!/bin/sh") (string-append "#!" (which "sh"))))
               (substitute* "tests/clar/fs.h"
                 (("/bin/cp") (which "cp"))
                 (("/bin/rm") (which "rm")))))
           ;; Run checks more verbosely.
           (replace 'check
             (lambda* (#:key tests? #:allow-other-keys)
               (when tests?
                 (invoke "./libgit2_clar" "-v" "-Q"))))
           (add-after 'unpack 'make-files-writable-for-tests
             (lambda _ (for-each make-file-writable (find-files ".")))))))
      (inputs
       (list libssh2 http-parser python-wrapper))
      (native-inputs
       (list pkg-config))
      (propagated-inputs
       ;; These two libraries are in 'Requires.private' in libgit2.pc.
       (list openssl zlib))
      (home-page "https://libgit2.github.com/")
      (synopsis "Library providing Git core methods")
      (description
       "Libgit2 is a portable, pure C implementation of the Git core methods
provided as a re-entrant linkable library with a solid API, allowing you to
write native speed custom Git applications in any language with bindings.")
      ;; GPLv2 with linking exception
      (license license:gpl2))))
@end lisp

(In those cases were you only want to tweak a few fields from a package
definition, you should rely on inheritance instead of copy-pasting everything.
See below.)

Let's discuss those fields in depth.

@subsubsection @code{git-fetch} method

Unlike the @code{url-fetch} method, @code{git-fetch} expects a @code{git-reference} which takes
a Git repository and a commit.  The commit can be any Git reference such as
tags, so if the @code{version} is tagged, then it can be used directly.  Sometimes
the tag is prefixed with a @code{v}, in which case you'd use @code{(commit (string-append
"v" version))}.

To ensure that the source code from the Git repository is stored in a
directory with a descriptive name, we use @code{(file-name (git-file-name name
version))}.

The @code{git-version} procedure can be used to derive the
version when packaging programs for a specific commit, following the
Guix contributor guidelines (@pxref{Version Numbers,,, guix, GNU Guix
Reference Manual}).

How does one obtain the @code{sha256} hash that's in there, you ask?  By
invoking @command{guix hash} on a checkout of the desired commit, along
these lines:

@example
git clone https://github.com/libgit2/libgit2/
cd libgit2
git checkout v0.26.6
guix hash -rx .
@end example

@command{guix hash -rx} computes a SHA256 hash over the whole directory,
excluding the @file{.git} sub-directory (@pxref{Invoking guix hash,,,
guix, GNU Guix Reference Manual}).

In the future, @command{guix download} will hopefully be able to do
these steps for you, just like it does for regular downloads.

@subsubsection Snippets

Snippets are quoted (i.e. non-evaluated) Scheme code that are a means of patching
the source.  They are a Guix-y alternative to the traditional @file{.patch} files.
Because of the quote, the code in only evaluated when passed to the Guix daemon
for building.  There can be as many snippets as needed.

Snippets might need additional Guile modules which can be imported from the
@code{modules} field.

@subsubsection Inputs

There are 3 different input types.  In short:

@table @asis
@item native-inputs
Required for building but not runtime -- installing a package
through a substitute won't install these inputs.
@item inputs
Installed in the store but not in the profile, as well as being
present at build time.
@item propagated-inputs
Installed in the store and in the profile, as well as
being present at build time.
@end table

@xref{package Reference,,, guix, GNU Guix Reference Manual} for more details.

The distinction between the various inputs is important: if a dependency can be
handled as an @emph{input} instead of a @emph{propagated input}, it should be done so, or
else it ``pollutes'' the user profile for no good reason.

For instance, a user installing a graphical program that depends on a
command line tool might only be interested in the graphical part, so there is no
need to force the command line tool into the user profile.  The dependency is a
concern to the package, not to the user.  @emph{Inputs} make it possible to handle
dependencies without bugging the user by adding undesired executable files (or
libraries) to their profile.

Same goes for @emph{native-inputs}: once the program is installed, build-time
dependencies can be safely garbage-collected.
It also matters when a substitute is available, in which case only the @emph{inputs}
and @emph{propagated inputs} will be fetched: the @emph{native inputs} are not required to
install a package from a substitute.

@quotation Note
You may see here and there snippets where package inputs are written
quite differently, like so:

@lisp
;; The "old style" for inputs.
(inputs
 `(("libssh2" ,libssh2)
   ("http-parser" ,http-parser)
   ("python" ,python-wrapper)))
@end lisp

This is the ``old style'', where each input in the list is explicitly
given a label (a string).  It is still supported but we recommend using
the style above instead.  @xref{package Reference,,, guix, GNU Guix
Reference Manual}, for more info.
@end quotation

@subsubsection Outputs

Just like how a package can have multiple inputs, it can also produce multiple
outputs.

Each output corresponds to a separate directory in the store.

The user can choose which output to install; this is useful to save space or
to avoid polluting the user profile with unwanted executables or libraries.

Output separation is optional.  When the @code{outputs} field is left out, the
default and only output (the complete package) is referred to as @code{"out"}.

Typical separate output names include @code{debug} and @code{doc}.

It's advised to separate outputs only when you've shown it's worth it: if the
output size is significant (compare with @code{guix size}) or in case the package is
modular.

@subsubsection Build system arguments

The @code{arguments} is a keyword-value list used to configure the build process.

The simplest argument @code{#:tests?} can be used to disable the test suite when
building the package.  This is mostly useful when the package does not feature
any test suite.  It's strongly recommended to keep the test suite on if there is
one.

Another  common argument is @code{:make-flags}, which specifies a list of flags to
append when running make, as you would from the command line.  For instance, the
following flags

@lisp
#:make-flags (list (string-append "prefix=" (assoc-ref %outputs "out"))
                   "CC=gcc")
@end lisp

translate into

@example
$ make CC=gcc prefix=/gnu/store/...-<out>
@end example

This sets the C compiler to @code{gcc} and the @code{prefix} variable (the installation
directory in Make parlance) to @code{(assoc-ref %outputs "out")}, which is a build-stage
global variable pointing to the destination directory in the store (something like
@file{/gnu/store/...-my-libgit2-20180408}).

Similarly, it's possible to set the configure flags:

@lisp
#:configure-flags '("-DUSE_SHA1DC=ON")
@end lisp

The @code{%build-inputs} variable is also generated in scope.  It's an association
table that maps the input names to their store directories.

The @code{phases} keyword lists the sequential steps of the build system.  Typically
phases include @code{unpack}, @code{configure}, @code{build}, @code{install} and @code{check}.  To know
more about those phases, you need to work out the appropriate build system
definition in @samp{$GUIX_CHECKOUT/guix/build/gnu-build-system.scm}:

@lisp
(define %standard-phases
  ;; Standard build phases, as a list of symbol/procedure pairs.
  (let-syntax ((phases (syntax-rules ()
                         ((_ p ...) `((p . ,p) ...)))))
    (phases set-SOURCE-DATE-EPOCH set-paths install-locale unpack
            bootstrap
            patch-usr-bin-file
            patch-source-shebangs configure patch-generated-file-shebangs
            build check install
            patch-shebangs strip
            validate-runpath
            validate-documentation-location
            delete-info-dir-file
            patch-dot-desktop-files
            install-license-files
            reset-gzip-timestamps
            compress-documentation)))
@end lisp

Or from the REPL:

@lisp
(add-to-load-path "/path/to/guix/checkout")
,use (guix build gnu-build-system)
(map first %standard-phases)
@result{} (set-SOURCE-DATE-EPOCH set-paths install-locale unpack bootstrap patch-usr-bin-file patch-source-shebangs configure patch-generated-file-shebangs build check install patch-shebangs strip validate-runpath validate-documentation-location delete-info-dir-file patch-dot-desktop-files install-license-files reset-gzip-timestamps compress-documentation)
@end lisp

If you want to know more about what happens during those phases, consult the
associated procedures.

For instance, as of this writing the definition of @code{unpack} for the GNU build
system is:

@lisp
(define* (unpack #:key source #:allow-other-keys)
  "Unpack SOURCE in the working directory, and change directory within the
source.  When SOURCE is a directory, copy it in a sub-directory of the current
working directory."
  (if (file-is-directory? source)
      (begin
        (mkdir "source")
        (chdir "source")

        ;; Preserve timestamps (set to the Epoch) on the copied tree so that
        ;; things work deterministically.
        (copy-recursively source "."
                          #:keep-mtime? #true))
      (begin
        (if (string-suffix? ".zip" source)
            (invoke "unzip" source)
            (invoke "tar" "xvf" source))
        (chdir (first-subdirectory "."))))
  #true)
@end lisp

Note the @code{chdir} call: it changes the working directory to where the source was
unpacked.
Thus every phase following the @code{unpack} will use the source as a working
directory, which is why we can directly work on the source files.
That is to say, unless a later phase changes the working directory to something
else.

We modify the list of @code{%standard-phases} of the build system with the
@code{modify-phases} macro as per the list of specified modifications, which may have
the following forms:

@itemize
@item
@code{(add-before @var{phase} @var{new-phase} @var{procedure})}: Run @var{procedure} named @var{new-phase} before @var{phase}.
@item
@code{(add-after @var{phase} @var{new-phase} @var{procedure})}: Same, but afterwards.
@item
@code{(replace @var{phase} @var{procedure})}.
@item
@code{(delete @var{phase})}.
@end itemize

The @var{procedure} supports the keyword arguments @code{inputs} and @code{outputs}.  Each
input (whether @emph{native}, @emph{propagated} or not) and output directory is referenced
by their name in those variables.  Thus @code{(assoc-ref outputs "out")} is the store
directory of the main output of the package.  A phase procedure may look like
this:

@lisp
(lambda* (#:key inputs outputs #:allow-other-keys)
  (let ((bash-directory (assoc-ref inputs "bash"))
        (output-directory (assoc-ref outputs "out"))
        (doc-directory (assoc-ref outputs "doc")))
    ;; ...
    #true))
@end lisp

The procedure must return @code{#true} on success.  It's brittle to rely on the return
value of the last expression used to tweak the phase because there is no
guarantee it would be a @code{#true}.  Hence the trailing @code{#true} to ensure the right value
is returned on success.

@subsubsection Code staging

The astute reader may have noticed the quasi-quote and comma syntax in the
argument field.  Indeed, the build code in the package declaration should not be
evaluated on the client side, but only when passed to the Guix daemon.  This
mechanism of passing code around two running processes is called @uref{https://arxiv.org/abs/1709.00833, code staging}.

@subsubsection Utility functions

When customizing @code{phases}, we often need to write code that mimics the
equivalent system invocations (@code{make}, @code{mkdir}, @code{cp}, etc.)@: commonly used during
regular ``Unix-style'' installations.

Some like @code{chmod} are native to Guile.
@xref{,,, guile, Guile reference manual} for a complete list.

Guix provides additional helper functions which prove especially handy in the
context of package management.

Some of those functions can be found in
@samp{$GUIX_CHECKOUT/guix/guix/build/utils.scm}.  Most of them mirror the behaviour
of the traditional Unix system commands:

@table @code
@item which
Like the @samp{which} system command.
@item find-files
Akin to the @samp{find} system command.
@item mkdir-p
Like @samp{mkdir -p}, which creates all parents as needed.
@item install-file
Similar to @samp{install} when installing a file to a (possibly
non-existing) directory.  Guile has @code{copy-file} which works
like @samp{cp}.
@item copy-recursively
Like @samp{cp -r}.
@item delete-file-recursively
Like @samp{rm -rf}.
@item invoke
Run an executable.  This should be used instead of @code{system*}.
@item with-directory-excursion
Run the body in a different working directory,
then restore the previous working directory.
@item substitute*
A ``@command{sed}-like'' function.
@end table

@xref{Build Utilities,,, guix, GNU Guix Reference Manual}, for more
information on these utilities.

@subsubsection Module prefix

The license in our last example needs a prefix: this is because of how the
@code{license} module was imported in the package, as @code{#:use-module ((guix licenses)
#:prefix license:)}.  The Guile module import mechanism
(@pxref{Using Guile Modules,,, guile, Guile reference manual})
gives the user full control over namespacing: this is needed to avoid
clashes between, say, the
@samp{zlib} variable from @samp{licenses.scm} (a @emph{license} value) and the @samp{zlib} variable
from @samp{compression.scm} (a @emph{package} value).

@node Other build systems
@subsection Other build systems

What we've seen so far covers the majority of packages using a build system
other than the @code{trivial-build-system}.  The latter does not automate anything
and leaves you to build everything manually.  This can be more demanding and we
won't cover it here for now, but thankfully it is rarely necessary to fall back
on this system.

For the other build systems, such as ASDF, Emacs, Perl, Ruby and many more, the
process is very similar to the GNU build system except for a few specialized
arguments.

@xref{Build Systems,,, guix, GNU Guix Reference Manual}, for more
information on build systems, or check the source code in the
@samp{$GUIX_CHECKOUT/guix/build} and
@samp{$GUIX_CHECKOUT/guix/build-system} directories.

@node Programmable and automated package definition
@subsection Programmable and automated package definition

We can't repeat it enough: having a full-fledged programming language at hand
empowers us in ways that reach far beyond traditional package management.

Let's illustrate this with some awesome features of Guix!

@menu
* Recursive importers::
* Automatic update::
* Inheritance::
@end menu

@node Recursive importers
@subsubsection Recursive importers

You might find some build systems good enough that there is little to do at all
to write a package, to the point that it becomes repetitive and tedious after a
while.  A @emph{raison d'être} of computers is to replace human beings at those
boring tasks.  So let's tell Guix to do this for us and create the package
definition of an R package from CRAN (the output is trimmed for conciseness):

@example
$ guix import cran --recursive walrus

(define-public r-mc2d
    ; ...
    (license gpl2+)))

(define-public r-jmvcore
    ; ...
    (license gpl2+)))

(define-public r-wrs2
    ; ...
    (license gpl3)))

(define-public r-walrus
  (package
    (name "r-walrus")
    (version "1.0.3")
    (source
      (origin
        (method url-fetch)
        (uri (cran-uri "walrus" version))
        (sha256
          (base32
            "1nk2glcvy4hyksl5ipq2mz8jy4fss90hx6cq98m3w96kzjni6jjj"))))
    (build-system r-build-system)
    (propagated-inputs
      (list r-ggplot2 r-jmvcore r-r6 r-wrs2))
    (home-page "https://github.com/jamovi/walrus")
    (synopsis "Robust Statistical Methods")
    (description
      "This package provides a toolbox of common robust statistical
tests, including robust descriptives, robust t-tests, and robust ANOVA.
It is also available as a module for 'jamovi' (see
<https://www.jamovi.org> for more information).  Walrus is based on the
WRS2 package by Patrick Mair, which is in turn based on the scripts and
work of Rand Wilcox.  These analyses are described in depth in the book
'Introduction to Robust Estimation & Hypothesis Testing'.")
    (license gpl3)))
@end example

The recursive importer won't import packages for which Guix already has package
definitions, except for the very first.

Not all applications can be packaged this way, only those relying on a select
number of supported systems.  Read about the full list of importers in
the guix import section of the manual
(@pxref{Invoking guix import,,, guix, GNU Guix Reference Manual}).

@node Automatic update
@subsubsection Automatic update

Guix can be smart enough to check for updates on systems it knows.  It can
report outdated package definitions with

@example
$ guix refresh hello
@end example

In most cases, updating a package to a newer version requires little more than
changing the version number and the checksum.  Guix can do that automatically as
well:

@example
$ guix refresh hello --update
@end example

@node Inheritance
@subsubsection Inheritance

If you've started browsing the existing package definitions, you might have
noticed that a significant number of them have a @code{inherit} field:

@lisp
(define-public adwaita-icon-theme
  (package (inherit gnome-icon-theme)
    (name "adwaita-icon-theme")
    (version "3.26.1")
    (source (origin
              (method url-fetch)
              (uri (string-append "mirror://gnome/sources/" name "/"
                                  (version-major+minor version) "/"
                                  name "-" version ".tar.xz"))
              (sha256
               (base32
                "17fpahgh5dyckgz7rwqvzgnhx53cx9kr2xw0szprc6bnqy977fi8"))))
    (native-inputs (list `(,gtk+ "bin")))))
@end lisp

All unspecified fields are inherited from the parent package.  This is very
convenient to create alternative packages, for instance with different source,
version or compilation options.

@node Getting help
@subsection Getting help

Sadly, some applications can be tough to package.  Sometimes they need a patch to
work with the non-standard file system hierarchy enforced by the store.
Sometimes the tests won't run properly.  (They can be skipped but this is not
recommended.)  Other times the resulting package won't be reproducible.

Should you be stuck, unable to figure out how to fix any sort of packaging
issue, don't hesitate to ask the community for help.

See the @uref{https://www.gnu.org/software/guix/contact/, Guix homepage} for information on the mailing lists, IRC, etc.

@node Conclusion
@subsection Conclusion

This tutorial was a showcase of the sophisticated package management that Guix
boasts.  At this point we have mostly restricted this introduction to the
@code{gnu-build-system} which is a core abstraction layer on which more advanced
abstractions are based.

Where do we go from here?  Next we ought to dissect the innards of the build
system by removing all abstractions, using the @code{trivial-build-system}: this
should give us a thorough understanding of the process before investigating some
more advanced packaging techniques and edge cases.

Other features worth exploring are the interactive editing and debugging
capabilities of Guix provided by the Guile REPL@.

Those fancy features are completely optional and can wait; now is a good time
to take a well-deserved break.  With what we've introduced here you should be
well armed to package lots of programs.  You can get started right away and
hopefully we will see your contributions soon!

@node References
@subsection References

@itemize
@item
The @uref{https://www.gnu.org/software/guix/manual/en/html_node/Defining-Packages.html, package reference in the manual}

@item
@uref{https://gitlab.com/pjotrp/guix-notes/blob/master/HACKING.org, Pjotr’s hacking guide to GNU Guix}

@item
@uref{https://www.gnu.org/software/guix/guix-ghm-andreas-20130823.pdf, ``GNU Guix: Package without a scheme!''}, by Andreas Enge
@end itemize

@c *********************************************************************
@node System Configuration
@chapter System Configuration

Guix offers a flexible language for declaratively configuring your Guix
System.  This flexibility can at times be overwhelming.  The purpose of this
chapter is to demonstrate some advanced configuration concepts.

@pxref{System Configuration,,, guix, GNU Guix Reference Manual} for a complete
reference.

@menu
* Auto-Login to a Specific TTY::  Automatically Login a User to a Specific TTY
* Customizing the Kernel::      Creating and using a custom Linux kernel on Guix System.
* Guix System Image API::       Customizing images to target specific platforms.
* Using security keys::         How to use security keys with Guix System.
* Dynamic DNS mcron job::       Job to update the IP address behind a DuckDNS host name.
* Connecting to Wireguard VPN::  Connecting to a Wireguard VPN.
* Customizing a Window Manager::  Handle customization of a Window manager on Guix System.
* Running Guix on a Linode Server::  Running Guix on a Linode Server.
* Running Guix on a Kimsufi Server::  Running Guix on a Kimsufi Server.
* Setting up a bind mount::     Setting up a bind mount in the file-systems definition.
* Getting substitutes from Tor::  Configuring Guix daemon to get substitutes through Tor.
* Setting up NGINX with Lua::   Configuring NGINX web-server to load Lua modules.
* Music Server with Bluetooth Audio::  Headless music player with Bluetooth output.
@end menu

@node Auto-Login to a Specific TTY
@section Auto-Login to a Specific TTY

While the Guix manual explains auto-login one user to @emph{all} TTYs (
@pxref{auto-login to TTY,,, guix, GNU Guix Reference Manual}), some
might prefer a situation, in which one user is logged into one TTY with
the other TTYs either configured to login different users or no one at
all.  Note that one can auto-login one user to any TTY, but it is
usually advisable to avoid @code{tty1}, which, by default, is used to
log warnings and errors.

Here is how one might set up auto login for one user to one tty:

@lisp
(define (auto-login-to-tty config tty user)
  (if (string=? tty (mingetty-configuration-tty config))
        (mingetty-configuration
         (inherit config)
         (auto-login user))
        config))

(define %my-services
  (modify-services %base-services
    ;; @dots{}
    (mingetty-service-type config =>
                           (auto-login-to-tty
                            config "tty3" "alice"))))

(operating-system
  ;; @dots{}
  (services %my-services))
@end lisp

One could also @code{compose} (@pxref{Higher-Order Functions,,, guile,
The Guile Reference Manual}) @code{auto-login-to-tty} to login multiple
users to multiple ttys.

Finally, here is a note of caution.  Setting up auto login to a TTY,
means that anyone can turn on your computer and run commands as your
regular user.
However, if you have an encrypted root partition, and thus already need
to enter a passphrase when the system boots, auto-login might be a
convenient option.


@node Customizing the Kernel
@section Customizing the Kernel

Guix is, at its core, a source based distribution with substitutes
(@pxref{Substitutes,,, guix, GNU Guix Reference Manual}), and as such building
packages from their source code is an expected part of regular package
installations and upgrades.  Given this starting point, it makes sense that
efforts are made to reduce the amount of time spent compiling packages, and
recent changes and upgrades to the building and distribution of substitutes
continues to be a topic of discussion within Guix.

The kernel, while not requiring an overabundance of RAM to build, does take a
rather long time on an average machine.  The official kernel configuration, as
is the case with many GNU/Linux distributions, errs on the side of
inclusiveness, and this is really what causes the build to take such a long
time when the kernel is built from source.

The Linux kernel, however, can also just be described as a regular old
package, and as such can be customized just like any other package.  The
procedure is a little bit different, although this is primarily due to the
nature of how the package definition is written.

The @code{linux-libre} kernel package definition is actually a procedure which
creates a package.

@lisp
(define* (make-linux-libre* version gnu-revision source supported-systems
                            #:key
                            (extra-version #f)
                            ;; A function that takes an arch and a variant.
                            ;; See kernel-config for an example.
                            (configuration-file #f)
                            (defconfig "defconfig")
                            (extra-options %default-extra-linux-options))
  ...)
@end lisp

The current @code{linux-libre} package is for the 5.15.x series, and is
declared like this:

@lisp
(define-public linux-libre-5.15
  (make-linux-libre* linux-libre-5.15-version
                     linux-libre-5.15-gnu-revision
                     linux-libre-5.15-source
                     '("x86_64-linux" "i686-linux" "armhf-linux" "aarch64-linux" "riscv64-linux")
                     #:configuration-file kernel-config))
@end lisp

Any keys which are not assigned values inherit their default value from the
@code{make-linux-libre} definition.  When comparing the two snippets above,
notice the code comment that refers to @code{#:configuration-file}.  Because of
this, it is not actually easy to include a custom kernel configuration from the
definition, but don't worry, there are other ways to work with what we do have.

There are two ways to create a kernel with a custom kernel configuration.  The
first is to provide a standard @file{.config} file during the build process by
including an actual @file{.config} file as a native input to our custom
kernel.  The following is a snippet from the custom @code{'configure} phase of
the @code{make-linux-libre} package definition:

@lisp
(let ((build  (assoc-ref %standard-phases 'build))
      (config (assoc-ref (or native-inputs inputs) "kconfig")))

  ;; Use a custom kernel configuration file or a default
  ;; configuration file.
  (if config
      (begin
        (copy-file config ".config")
        (chmod ".config" #o666))
      (invoke "make" ,defconfig)))
@end lisp

Below is a sample kernel package.  The @code{linux-libre} package is nothing
special and can be inherited from and have its fields overridden like any
other package:

@lisp
(define-public linux-libre/E2140
  (package
    (inherit linux-libre)
    (native-inputs
     `(("kconfig" ,(local-file "E2140.config"))
      ,@@(alist-delete "kconfig"
                      (package-native-inputs linux-libre))))))
@end lisp

In the same directory as the file defining @code{linux-libre-E2140} is a file
named @file{E2140.config}, which is an actual kernel configuration file.  The
@code{defconfig} keyword of @code{make-linux-libre} is left blank here, so the
only kernel configuration in the package is the one which was included in the
@code{native-inputs} field.

The second way to create a custom kernel is to pass a new value to the
@code{extra-options} keyword of the @code{make-linux-libre} procedure.  The
@code{extra-options} keyword works with another function defined right below
it:

@lisp
(define %default-extra-linux-options
  `(;; https://lists.gnu.org/archive/html/guix-devel/2014-04/msg00039.html
   ("CONFIG_DEVPTS_MULTIPLE_INSTANCES" . #true)
   ;; Modules required for initrd:
   ("CONFIG_NET_9P" . m)
   ("CONFIG_NET_9P_VIRTIO" . m)
   ("CONFIG_VIRTIO_BLK" . m)
   ("CONFIG_VIRTIO_NET" . m)
   ("CONFIG_VIRTIO_PCI" . m)
   ("CONFIG_VIRTIO_BALLOON" . m)
   ("CONFIG_VIRTIO_MMIO" . m)
   ("CONFIG_FUSE_FS" . m)
   ("CONFIG_CIFS" . m)
   ("CONFIG_9P_FS" . m)))

(define (config->string options)
  (string-join (map (match-lambda
                      ((option . 'm)
                       (string-append option "=m"))
                      ((option . #true)
                       (string-append option "=y"))
                      ((option . #false)
                       (string-append option "=n")))
                    options)
               "\n"))
@end lisp

And in the custom configure script from the `make-linux-libre` package:

@lisp
;; Appending works even when the option wasn't in the
;; file.  The last one prevails if duplicated.
(let ((port (open-file ".config" "a"))
      (extra-configuration ,(config->string extra-options)))
  (display extra-configuration port)
  (close-port port))

(invoke "make" "oldconfig")
@end lisp

So by not providing a configuration-file the @file{.config} starts blank, and
then we write into it the collection of flags that we want.  Here's another
custom kernel:

@lisp
(define %macbook41-full-config
  (append %macbook41-config-options
          %file-systems
          %efi-support
          %emulation
          (@@@@ (gnu packages linux) %default-extra-linux-options)))

(define-public linux-libre-macbook41
  ;; XXX: Access the internal 'make-linux-libre*' procedure, which is
  ;; private and unexported, and is liable to change in the future.
  ((@@@@ (gnu packages linux) make-linux-libre*)
   (@@@@ (gnu packages linux) linux-libre-version)
   (@@@@ (gnu packages linux) linux-libre-gnu-revision)
   (@@@@ (gnu packages linux) linux-libre-source)
   '("x86_64-linux")
   #:extra-version "macbook41"
   #:extra-options %macbook41-config-options))
@end lisp

In the above example @code{%file-systems} is a collection of flags enabling
different file system support, @code{%efi-support} enables EFI support and
@code{%emulation} enables a x86_64-linux machine to act in 32-bit mode also.
@code{%default-extra-linux-options} are the ones quoted above, which had to be
added in since they were replaced in the @code{extra-options} keyword.

This all sounds like it should be doable, but how does one even know which
modules are required for a particular system?  Two places that can be helpful
in trying to answer this question is the
@uref{https://wiki.gentoo.org/wiki/Handbook:AMD64/Installation/Kernel, Gentoo
Handbook} and the
@uref{https://www.kernel.org/doc/html/latest/admin-guide/README.html?highlight=localmodconfig,
documentation from the kernel itself}.  From the kernel documentation, it
seems that @code{make localmodconfig} is the command we want.

In order to actually run @code{make localmodconfig} we first need to get and
unpack the kernel source code:

@example shell
tar xf $(guix build linux-libre --source)
@end example

Once inside the directory containing the source code run @code{touch .config}
to create an initial, empty @file{.config} to start with.  @code{make
localmodconfig} works by seeing what you already have in @file{.config} and
letting you know what you're missing.  If the file is blank then you're
missing everything.  The next step is to run:

@example shell
guix shell -D linux-libre -- make localmodconfig
@end example

and note the output.  Do note that the @file{.config} file is still empty.
The output generally contains two types of warnings.  The first start with
"WARNING" and can actually be ignored in our case.  The second read:

@example shell
module pcspkr did not have configs CONFIG_INPUT_PCSPKR
@end example

For each of these lines, copy the @code{CONFIG_XXXX_XXXX} portion into the
@file{.config} in the directory, and append @code{=m}, so in the end it looks
like this:

@example shell
CONFIG_INPUT_PCSPKR=m
CONFIG_VIRTIO=m
@end example

After copying all the configuration options, run @code{make localmodconfig}
again to make sure that you don't have any output starting with ``module''.
After all of these machine specific modules there are a couple more left that
are also needed.  @code{CONFIG_MODULES} is necessary so that you can build and
load modules separately and not have everything built into the kernel.
@code{CONFIG_BLK_DEV_SD} is required for reading from hard drives.  It is
possible that there are other modules which you will need.

This post does not aim to be a guide to configuring your own kernel however,
so if you do decide to build a custom kernel you'll have to seek out other
guides to create a kernel which is just right for your needs.

The second way to setup the kernel configuration makes more use of Guix's
features and allows you to share configuration segments between different
kernels.  For example, all machines using EFI to boot have a number of EFI
configuration flags that they need.  It is likely that all the kernels will
share a list of file systems to support.  By using variables it is easier to
see at a glance what features are enabled and to make sure you don't have
features in one kernel but missing in another.

Left undiscussed however, is Guix's initrd and its customization.  It is
likely that you'll need to modify the initrd on a machine using a custom
kernel, since certain modules which are expected to be built may not be
available for inclusion into the initrd.

@node Guix System Image API
@section Guix System Image API

Historically, Guix System is centered around an @code{operating-system}
structure.  This structure contains various fields ranging from the
bootloader and kernel declaration to the services to install.

Depending on the target machine, that can go from a standard
@code{x86_64} machine to a small ARM single board computer such as the
Pine64, the image constraints can vary a lot.  The hardware
manufacturers will impose different image formats with various partition
sizes and offsets.

To create images suitable for all those machines, a new abstraction is
necessary: that's the goal of the @code{image} record.  This record
contains all the required information to be transformed into a
standalone image, that can be directly booted on any target machine.

@lisp
(define-record-type* <image>
  image make-image
  image?
  (name               image-name ;symbol
                      (default #f))
  (format             image-format) ;symbol
  (target             image-target
                      (default #f))
  (size               image-size  ;size in bytes as integer
                      (default 'guess))
  (operating-system   image-operating-system  ;<operating-system>
                      (default #f))
  (partitions         image-partitions ;list of <partition>
                      (default '()))
  (compression?       image-compression? ;boolean
                      (default #t))
  (volatile-root?     image-volatile-root? ;boolean
                      (default #t))
  (substitutable?     image-substitutable? ;boolean
                      (default #t)))
@end lisp

This record contains the operating-system to instantiate. The
@code{format} field defines the image type and can be @code{efi-raw},
@code{qcow2} or @code{iso9660} for instance. In the future, it could be
extended to @code{docker} or other image types.

A new directory in the Guix sources is dedicated to images definition. For now
there are four files:

@itemize @bullet
@item @file{gnu/system/images/hurd.scm}
@item @file{gnu/system/images/pine64.scm}
@item @file{gnu/system/images/novena.scm}
@item @file{gnu/system/images/pinebook-pro.scm}
@end itemize

Let's have a look to @file{pine64.scm}. It contains the
@code{pine64-barebones-os} variable which is a minimal definition of an
operating-system dedicated to the @b{Pine A64 LTS} board.

@lisp
(define pine64-barebones-os
  (operating-system
   (host-name "vignemale")
   (timezone "Europe/Paris")
   (locale "en_US.utf8")
   (bootloader (bootloader-configuration
                (bootloader u-boot-pine64-lts-bootloader)
                (targets '("/dev/vda"))))
   (initrd-modules '())
   (kernel linux-libre-arm64-generic)
   (file-systems (cons (file-system
                        (device (file-system-label "my-root"))
                        (mount-point "/")
                        (type "ext4"))
                       %base-file-systems))
   (services (cons (service agetty-service-type
                            (agetty-configuration
                             (extra-options '("-L")) ; no carrier detect
                             (baud-rate "115200")
                             (term "vt100")
                             (tty "ttyS0")))
                   %base-services))))
@end lisp

The @code{kernel} and @code{bootloader} fields are pointing to packages
dedicated to this board.

Right below, the @code{pine64-image-type} variable is also defined.

@lisp
(define pine64-image-type
  (image-type
   (name 'pine64-raw)
   (constructor (cut image-with-os arm64-disk-image <>))))
@end lisp

It's using a record we haven't talked about yet, the @code{image-type} record,
defined this way:

@lisp
(define-record-type* <image-type>
  image-type make-image-type
  image-type?
  (name           image-type-name) ;symbol
  (constructor    image-type-constructor)) ;<operating-system> -> <image>
@end lisp

The main purpose of this record is to associate a name to a procedure
transforming an @code{operating-system} to an image.  To understand why
it is necessary, let's have a look to the command producing an image
from an @code{operating-system} configuration file:

@example
guix system image my-os.scm
@end example

This command expects an @code{operating-system} configuration but how
should we indicate that we want an image targeting a Pine64 board?  We
need to provide an extra information, the @code{image-type}, by passing
the @code{--image-type} or @code{-t} flag, this way:

@example
guix system image --image-type=pine64-raw my-os.scm
@end example

This @code{image-type} parameter points to the @code{pine64-image-type}
defined above. Hence, the @code{operating-system} declared in
@code{my-os.scm} will be applied the @code{(cut image-with-os
arm64-disk-image <>)} procedure to turn it into an image.

The resulting image looks like:

@lisp
(image
 (format 'disk-image)
 (target "aarch64-linux-gnu")
 (operating-system my-os)
 (partitions
  (list (partition
         (inherit root-partition)
         (offset root-offset)))))
@end lisp

which is the aggregation of the @code{operating-system} defined in
 @code{my-os.scm} to the @code{arm64-disk-image} record.

But enough Scheme madness. What does this image API bring to the Guix user?

One can run:

@example
mathieu@@cervin:~$ guix system --list-image-types
The available image types are:

   - unmatched-raw
   - rock64-raw
   - pinebook-pro-raw
   - pine64-raw
   - novena-raw
   - hurd-raw
   - hurd-qcow2
   - qcow2
   - iso9660
   - uncompressed-iso9660
   - tarball
   - efi-raw
   - mbr-raw
   - docker
   - wsl2
   - raw-with-offset
   - efi32-raw
@end example

and by writing an @code{operating-system} file based on
@code{pine64-barebones-os}, you can customize your image to your
preferences in a file (@file{my-pine-os.scm}) like this:

@lisp
(use-modules (gnu services linux)
             (gnu system images pine64))

(let ((base-os pine64-barebones-os))
  (operating-system
    (inherit base-os)
    (timezone "America/Indiana/Indianapolis")
    (services
     (cons
      (service earlyoom-service-type
               (earlyoom-configuration
                (prefer-regexp "icecat|chromium")))
      (operating-system-user-services base-os)))))
@end lisp

run:

@example
guix system image --image-type=pine64-raw my-pine-os.scm
@end example

or,

@example
guix system image --image-type=hurd-raw my-hurd-os.scm
@end example

to get an image that can be written directly to a hard drive and booted
from.

Without changing anything to @code{my-hurd-os.scm}, calling:

@example
guix system image --image-type=hurd-qcow2 my-hurd-os.scm
@end example

will instead produce a Hurd QEMU image.

@node Using security keys
@section Using security keys
@cindex 2FA, two-factor authentication
@cindex U2F, Universal 2nd Factor
@cindex security key, configuration

The use of security keys can improve your security by providing a second
authentication source that cannot be easily stolen or copied, at least
for a remote adversary (something that you have), to the main secret (a
passphrase -- something that you know), reducing the risk of
impersonation.

The example configuration detailed below showcases what minimal
configuration needs to be made on your Guix System to allow the use of a
Yubico security key.  It is hoped the configuration can be useful for
other security keys as well, with minor adjustments.

@subsection Configuration for use as a two-factor authenticator (2FA)

To be usable, the udev rules of the system should be extended with
key-specific rules.  The following shows how to extend your udev rules
with the @file{lib/udev/rules.d/70-u2f.rules} udev rule file provided by
the @code{libfido2} package from the @code{(gnu packages
security-token)} module and add your user to the @samp{"plugdev"} group
it uses:

@lisp
(use-package-modules ... security-token ...)
...
(operating-system
 ...
 (users (cons* (user-account
               (name "your-user")
               (group "users")
               (supplementary-groups
		'("wheel" "netdev" "audio" "video"
                  "plugdev"))           ;<- added system group
               (home-directory "/home/your-user"))
              %base-user-accounts))
 ...
 (services
  (cons*
   ...
   (udev-rules-service 'fido2 libfido2 #:groups '("plugdev")))))
@end lisp

After re-configuring your system and re-logging in your graphical
session so that the new group is in effect for your user, you can verify
that your key is usable by launching:

@example
guix shell ungoogled-chromium -- chromium chrome://settings/securityKeys
@end example

and validating that the security key can be reset via the ``Reset your
security key'' menu.  If it works, congratulations, your security key is
ready to be used with applications supporting two-factor authentication
(2FA).

@subsection Disabling OTP code generation for a Yubikey
@cindex disabling yubikey OTP
If you use a Yubikey security key and are irritated by the spurious OTP
codes it generates when inadvertently touching the key (e.g. causing you
to become a spammer in the @samp{#guix} channel when discussing from
your favorite IRC client!), you can disable it via the following
@command{ykman} command:

@example
guix shell python-yubikey-manager -- ykman config usb --force --disable OTP
@end example

Alternatively, you could use the @command{ykman-gui} command provided by
the @code{yubikey-manager-qt} package and either wholly disable the
@samp{OTP} application for the USB interface or, from the
@samp{Applications -> OTP} view, delete the slot 1 configuration, which
comes pre-configured with the Yubico OTP application.

@subsection Requiring a Yubikey to open a KeePassXC database
@cindex yubikey, keepassxc integration
The KeePassXC password manager application has support for Yubikeys, but
it requires installing a udev rules for your Guix System and some
configuration of the Yubico OTP application on the key.

The necessary udev rules file comes from the
@code{yubikey-personalization} package, and can be installed like:

@lisp
(use-package-modules ... security-token ...)
...
(operating-system
 ...
 (services
  (cons*
   ...
   (udev-rules-service 'yubikey yubikey-personalization))))
@end lisp

After reconfiguring your system (and reconnecting your Yubikey), you'll
then want to configure the OTP challenge/response application of your
Yubikey on its slot 2, which is what KeePassXC uses.  It's easy to do so
via the Yubikey Manager graphical configuration tool, which can be
invoked with:

@example
guix shell yubikey-manager-qt -- ykman-gui
@end example

First, ensure @samp{OTP} is enabled under the @samp{Interfaces} tab,
then navigate to @samp{Applications -> OTP}, and click the
@samp{Configure} button under the @samp{Long Touch (Slot 2)} section.
Select @samp{Challenge-response}, input or generate a secret key, and
click the @samp{Finish} button.  If you have a second Yubikey you'd like
to use as a backup, you should configure it the same way, using the
@emph{same} secret key.

Your Yubikey should now be detected by KeePassXC.  It can be added to a
database by navigating to KeePassXC's @samp{Database -> Database
Security...}  menu, then clicking the @samp{Add additional
protection...} button, then @samp{Add Challenge-Response}, selecting the
security key from the drop-down menu and clicking the @samp{OK} button
to complete the setup.

@node Dynamic DNS mcron job
@section Dynamic DNS mcron job

@cindex dynamic DNS, DDNS
If your @acronym{ISP, Internet Service Provider} only provides dynamic
IP addresses, it can be useful to setup a dynamic @acronym{DNS, Domain
Name System} (also known as @acronym{DDNS, Dynamic DNS}) service to
associate a static host name to a public but dynamic (often changing) IP
address.  There are multiple existing services that can be used for
this; in the following mcron job, @url{https://duckdns.org, DuckDNS} is
used.  It should also work with other dynamic DNS services that offer a
similar interface to update the IP address, such as
@url{https://freedns.afraid.org/}, with minor adjustments.

The mcron job is provided below, where @var{DOMAIN} should be
substituted for your own domain prefix, and the DuckDNS provided token
associated to @var{DOMAIN} added to the
@file{/etc/duckdns/@var{DOMAIN}.token} file.

@lisp
(define duckdns-job
  ;; Update personal domain IP every 5 minutes.
  #~(job '(next-minute (range 0 60 5))
	 #$(program-file
            "duckdns-update"
            (with-extensions (list guile-gnutls) ;required by (web client)
              #~(begin
                  (use-modules (ice-9 textual-ports)
                               (web client))
                  (let ((token (string-trim-both
                                (call-with-input-file "/etc/duckdns/@var{DOMAIN}.token"
                                  get-string-all)))
                        (query-template (string-append "https://www.duckdns.org/"
                                                       "update?domains=@var{DOMAIN}"
                                                       "&token=~a&ip=")))
                    (http-get (format #f query-template token))))))
         "duckdns-update"
         #:user "nobody"))
@end lisp

The job then needs to be added to the list of mcron jobs for your
system, using something like:

@lisp
(operating-system
 (services
  (cons* (service mcron-service-type
           (mcron-configuration
             (jobs (list duckdns-job ...))))
         ...
         %base-services)))
@end lisp

@node Connecting to Wireguard VPN
@section Connecting to Wireguard VPN

To connect to a Wireguard VPN server you need the kernel module to be
loaded in memory and a package providing networking tools that support
it (e.g.  @code{wireguard-tools} or @code{network-manager}).

Here is a configuration example for Linux-Libre < 5.6, where the module
is out of tree and need to be loaded manually---following revisions of
the kernel have it built-in and so don't need such configuration:

@lisp
(use-modules (gnu))
(use-service-modules desktop)
(use-package-modules vpn)

(operating-system
  ;; …
  (services (cons (simple-service 'wireguard-module
                                  kernel-module-loader-service-type
                                  '("wireguard"))
                  %desktop-services))
  (packages (cons wireguard-tools %base-packages))
  (kernel-loadable-modules (list wireguard-linux-compat)))
@end lisp

After reconfiguring and restarting your system you can either use
Wireguard tools or NetworkManager to connect to a VPN server.

@subsection Using Wireguard tools

To test your Wireguard setup it is convenient to use @command{wg-quick}.
Just give it a configuration file @command{wg-quick up ./wg0.conf}; or
put that file in @file{/etc/wireguard} and run @command{wg-quick up wg0}
instead.

@quotation Note
Be warned that the author described this command as a: “[…] very quick
and dirty bash script […]”.
@end quotation

@subsection Using NetworkManager

Thanks to NetworkManager support for Wireguard we can connect to our VPN
using @command{nmcli} command.  Up to this point this guide assumes that
you're using Network Manager service provided by
@code{%desktop-services}.  Ortherwise you need to adjust your services
list to load @code{network-manager-service-type} and reconfigure your
Guix system.

To import your VPN configuration execute nmcli import command:

@example shell
# nmcli connection import type wireguard file wg0.conf
Connection 'wg0' (edbee261-aa5a-42db-b032-6c7757c60fde) successfully added
@end example

This will create a configuration file in
@file{/etc/NetworkManager/wg0.nmconnection}.  Next connect to the
Wireguard server:

@example shell
$ nmcli connection up wg0
Connection successfully activated (D-Bus active path: /org/freedesktop/NetworkManager/ActiveConnection/6)
@end example

By default NetworkManager will connect automatically on system boot.  To
change that behaviour you need to edit your config:

@example shell
# nmcli connection modify wg0 connection.autoconnect no
@end example

For more specific information about NetworkManager and wireguard
@uref{https://blogs.gnome.org/thaller/2019/03/15/wireguard-in-networkmanager/,see
this post by thaller}.

@node Customizing a Window Manager
@section Customizing a Window Manager
@cindex wm

@menu
* StumpWM::
* Session lock::
@end menu

@node StumpWM
@subsection StumpWM
@cindex stumpwm

You could install StumpWM with a Guix system by adding
@code{stumpwm} and optionally @code{`(,stumpwm "lib")}
packages to a system configuration file, e.g.@: @file{/etc/config.scm}.

An example configuration can look like this:

@lisp
(use-modules (gnu))
(use-package-modules wm)

(operating-system
  ;; …
  (packages (append (list sbcl stumpwm `(,stumpwm "lib"))
                    %base-packages)))
@end lisp

@cindex stumpwm fonts
By default StumpWM uses X11 fonts, which could be small or pixelated on
your system.  You could fix this by installing StumpWM contrib Lisp
module @code{sbcl-ttf-fonts}, adding it to Guix system packages:

@lisp
(use-modules (gnu))
(use-package-modules fonts wm)

(operating-system
  ;; …
  (packages (append (list sbcl stumpwm `(,stumpwm "lib"))
                    sbcl-ttf-fonts font-dejavu %base-packages)))
@end lisp

Then you need to add the following code to a StumpWM configuration file
@file{~/.stumpwm.d/init.lisp}:

@lisp
(require :ttf-fonts)
(setf xft:*font-dirs* '("/run/current-system/profile/share/fonts/"))
(setf clx-truetype:+font-cache-filename+ (concat (getenv "HOME") "/.fonts/font-cache.sexp"))
(xft:cache-fonts)
(set-font (make-instance 'xft:font :family "DejaVu Sans Mono" :subfamily "Book" :size 11))
@end lisp

@node Session lock
@subsection Session lock
@cindex sessionlock

Depending on your environment, locking the screen of your session might come built in
or it might be something you have to set up yourself. If you use a desktop environment
like GNOME or KDE, it's usually built in. If you use a plain window manager like
StumpWM or EXWM, you might have to set it up yourself.

@menu
* Xorg::
@end menu

@node Xorg
@subsubsection Xorg

If you use Xorg, you can use the utility
@uref{https://www.mankier.com/1/xss-lock, xss-lock} to lock the screen of your session.
xss-lock is triggered by DPMS which since Xorg 1.8 is auto-detected and enabled if
ACPI is also enabled at kernel runtime.

To use xss-lock, you can simple execute it and put it into the background before
you start your window manager from e.g. your @file{~/.xsession}:

@example
xss-lock -- slock &
exec stumpwm
@end example

In this example, xss-lock uses @code{slock} to do the actual locking of the screen when
it determines it's appropriate, like when you suspend your device.

For slock to be allowed to be a screen locker for the graphical session, it needs to
be made setuid-root so it can authenticate users, and it needs a PAM service. This
can be achieved by adding the following service to your @file{config.scm}:

@lisp
(service screen-locker-services-type
         (screen-locker-configuration
          (name "slock")
          (program (file-append slock "/bin/slock"))))
@end lisp

If you manually lock your screen, e.g. by directly calling slock when you want to lock
your screen but not suspend it, it's a good idea to notify xss-lock about this so no
confusion occurs. This can be done by executing @code{xset s activate} immediately
before you execute slock.

@node Running Guix on a Linode Server
@section Running Guix on a Linode Server
@cindex linode, Linode

To run Guix on a server hosted by @uref{https://www.linode.com, Linode},
start with a recommended Debian server.  We recommend using the default
distro as a way to bootstrap Guix. Create your SSH keys.

@example
ssh-keygen
@end example

Be sure to add your SSH key for easy login to the remote server.
This is trivially done via Linode's graphical interface for adding
SSH keys.  Go to your profile and click add SSH Key.
Copy into it the output of:

@example
cat ~/.ssh/<username>_rsa.pub
@end example

Power the Linode down.

In the Linode's Storage tab, resize the Debian disk to be smaller.
30 GB free space is recommended.  Then click "Add a disk", and fill
out the form with the following:

@itemize @bullet
@item
Label: "Guix"

@item
Filesystem: ext4

@item
Set it to the remaining size
@end itemize

In the Configurations tab, press "Edit" on the default Debian profile.
Under "Block Device Assignment" click "Add a Device". It should be
@file{/dev/sdc} and you can select the "Guix" disk. Save Changes.

Now "Add a Configuration", with the following:
@itemize @bullet
@item
Label: Guix

@item
Kernel:GRUB 2 (it's at the bottom!  This step is @b{IMPORTANT!})

@item
Block device assignment:

@item
@file{/dev/sda}: Guix

@item
@file{/dev/sdb}: swap

@item
Root device: @file{/dev/sda}

@item
Turn off all the filesystem/boot helpers
@end itemize

Now power it back up, booting with the Debian configuration.  Once it's
running, ssh to your server via @code{ssh
root@@@var{<your-server-IP-here>}}. (You can find your server IP address in
your Linode Summary section.) Now you can run the "install guix from
@pxref{Binary Installation,,, guix, GNU Guix}" steps:

@example
sudo apt-get install gpg
wget https://sv.gnu.org/people/viewgpg.php?user_id=15145 -qO - | gpg --import -
wget https://git.savannah.gnu.org/cgit/guix.git/plain/etc/guix-install.sh
chmod +x guix-install.sh
./guix-install.sh
guix pull
@end example

Now it's time to write out a config for the server.  The key information
is below. Save the resulting file as @file{guix-config.scm}.

@lisp
(use-modules (gnu)
             (guix modules))
(use-service-modules networking
                     ssh)
(use-package-modules admin
                     certs
                     package-management
                     ssh
                     tls)

(operating-system
  (host-name "my-server")
  (timezone "America/New_York")
  (locale "en_US.UTF-8")
  ;; This goofy code will generate the grub.cfg
  ;; without installing the grub bootloader on disk.
  (bootloader (bootloader-configuration
               (bootloader
                (bootloader
                 (inherit grub-bootloader)
                 (installer #~(const #true))))))
  (file-systems (cons (file-system
                        (device "/dev/sda")
                        (mount-point "/")
                        (type "ext4"))
                      %base-file-systems))


  (swap-devices (list "/dev/sdb"))


  (initrd-modules (cons "virtio_scsi"    ; Needed to find the disk
                        %base-initrd-modules))

  (users (cons (user-account
                (name "janedoe")
                (group "users")
                ;; Adding the account to the "wheel" group
                ;; makes it a sudoer.
                (supplementary-groups '("wheel"))
                (home-directory "/home/janedoe"))
               %base-user-accounts))

  (packages (cons* nss-certs            ;for HTTPS access
                   openssh-sans-x
                   %base-packages))

  (services (cons*
             (service dhcp-client-service-type)
             (service openssh-service-type
                      (openssh-configuration
                       (openssh openssh-sans-x)
                       (password-authentication? #false)
                       (authorized-keys
                        `(("janedoe" ,(local-file "janedoe_rsa.pub"))
                          ("root" ,(local-file "janedoe_rsa.pub"))))))
             %base-services)))
@end lisp

Replace the following fields in the above configuration:
@lisp
(host-name "my-server")       ; replace with your server name
; if you chose a linode server outside the U.S., then
; use tzselect to find a correct timezone string
(timezone "America/New_York") ; if needed replace timezone
(name "janedoe")              ; replace with your username
("janedoe" ,(local-file "janedoe_rsa.pub")) ; replace with your ssh key
("root" ,(local-file "janedoe_rsa.pub")) ; replace with your ssh key
@end lisp

The last line in the above example lets you log into the server as root
and set the initial root password (see the note at the end of this
recipe about root login).  After you have done this, you may
delete that line from your configuration and reconfigure to prevent root
login.

Copy your ssh public key (eg: @file{~/.ssh/id_rsa.pub}) as
@file{@var{<your-username-here>}_rsa.pub} and put
@file{guix-config.scm} in the same directory.  In a new terminal run
these commands.

@example
sftp root@@<remote server ip address>
put /path/to/files/<username>_rsa.pub .
put /path/to/files/guix-config.scm .
@end example

In your first terminal, mount the guix drive:

@example
mkdir /mnt/guix
mount /dev/sdc /mnt/guix
@end example

Due to the way we set up the bootloader section of the guix-config.scm,
only the grub configuration file will be installed.  So, we need to copy
over some of the other GRUB stuff already installed on the Debian system:

@example
mkdir -p /mnt/guix/boot/grub
cp -r /boot/grub/* /mnt/guix/boot/grub/
@end example

Now initialize the Guix installation:

@example
guix system init guix-config.scm /mnt/guix
@end example

Ok, power it down!
Now from the Linode console, select boot and select "Guix".

Once it boots, you should be able to log in via SSH!  (The server config
will have changed though.)  You may encounter an error like:

@example
$ ssh root@@<server ip address>
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@    WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!     @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that a host key has just been changed.
The fingerprint for the ECDSA key sent by the remote host is
SHA256:0B+wp33w57AnKQuHCvQP0+ZdKaqYrI/kyU7CfVbS7R4.
Please contact your system administrator.
Add correct host key in /home/joshua/.ssh/known_hosts to get rid of this message.
Offending ECDSA key in /home/joshua/.ssh/known_hosts:3
ECDSA host key for 198.58.98.76 has changed and you have requested strict checking.
Host key verification failed.
@end example

Either delete @file{~/.ssh/known_hosts} file, or delete the offending line
starting with your server IP address.

Be sure to set your password and root's password.

@example
ssh root@@<remote ip address>
passwd  ; for the root password
passwd <username> ; for the user password
@end example

You may not be able to run the above commands at this point.  If you
have issues remotely logging into your linode box via SSH, then you may
still need to set your root and user password initially by clicking on
the ``Launch Console'' option in your linode.  Choose the ``Glish''
instead of ``Weblish''.  Now you should be able to ssh into the machine.

Hooray!  At this point you can shut down the server, delete the
Debian disk, and resize the Guix to the rest of the size.
Congratulations!

By the way, if you save it as a disk image right at this point, you'll
have an easy time spinning up new Guix images!  You may need to
down-size the Guix image to 6144MB, to save it as an image.  Then you
can resize it again to the max size.

@node Running Guix on a Kimsufi Server
@section Running Guix on a Kimsufi Server
@cindex kimsufi, Kimsufi, OVH

To run Guix on a server hosted by @uref{https://www.kimsufi.com/,
Kimsufi}, click on the netboot tab then select rescue64-pro and restart.

OVH will email you the credentials required to ssh into a Debian system.

Now you can run the "install guix from @pxref{Binary Installation,,,
guix, GNU Guix}" steps:

@example
wget https://git.savannah.gnu.org/cgit/guix.git/plain/etc/guix-install.sh
chmod +x guix-install.sh
./guix-install.sh
guix pull
@end example

Partition the drives and format them, first stop the raid array:

@example
mdadm --stop /dev/md127
mdadm --zero-superblock /dev/sda2 /dev/sdb2
@end example

Then wipe the disks and set up the partitions, we will create
a RAID 1 array.

@example
wipefs -a /dev/sda
wipefs -a /dev/sdb

parted /dev/sda --align=opt -s -m -- mklabel gpt
parted /dev/sda --align=opt -s -m -- \
 mkpart bios_grub 1049kb 512MiB \
 set 1 bios_grub on
parted /dev/sda --align=opt -s -m -- \
 mkpart primary 512MiB -512MiB
 set 2 raid on
parted /dev/sda --align=opt -s -m -- mkpart primary linux-swap 512MiB 100%

parted /dev/sdb --align=opt -s -m -- mklabel gpt
parted /dev/sdb --align=opt -s -m -- \
     mkpart bios_grub 1049kb 512MiB \
     set 1 bios_grub on
parted /dev/sdb --align=opt -s -m -- \
     mkpart primary 512MiB -512MiB \
     set 2 raid on
parted /dev/sdb --align=opt -s -m -- mkpart primary linux-swap 512MiB 100%
@end example

Create the array:

@example
mdadm --create /dev/md127 --level=1 --raid-disks=2 \
  --metadata=0.90 /dev/sda2 /dev/sdb2
@end example

Now create file systems on the relevant partitions, first the boot
partitions:

@example
mkfs.ext4  /dev/sda1
mkfs.ext4  /dev/sdb1
@end example

Then the root partition:

@example
mkfs.ext4 /dev/md127
@end example

Initialize the swap partitions:

@example
mkswap /dev/sda3
swapon /dev/sda3
mkswap /dev/sdb3
swapon /dev/sdb3
@end example

Mount the guix drive:

@example
mkdir /mnt/guix
mount /dev/md127 /mnt/guix
@end example

Now is time to write an operating system declaration @file{os.scm} file;
here is a sample:

@lisp
(use-modules (gnu) (guix))
(use-service-modules networking ssh vpn virtualization sysctl admin mcron)
(use-package-modules ssh certs tls tmux vpn virtualization)

(operating-system
  (host-name "kimsufi")

  (bootloader (bootloader-configuration
	       (bootloader grub-bootloader)
	       (targets (list "/dev/sda" "/dev/sdb"))
	       (terminal-outputs '(console))))

  ;; Add a kernel module for RAID-1 (aka. "mirror").
  (initrd-modules (cons* "raid1"  %base-initrd-modules))

  (mapped-devices
   (list (mapped-device
          (source (list "/dev/sda2" "/dev/sdb2"))
          (target "/dev/md127")
          (type raid-device-mapping))))

  (swap-devices
   (list (swap-space
          (target "/dev/sda3"))
         (swap-space
          (target "/dev/sdb3"))))

  (issue
   ;; Default contents for /etc/issue.
   "\
This is the GNU system at Kimsufi.  Welcome.\n")

  (file-systems (cons* (file-system
		         (mount-point "/")
		         (device "/dev/md127")
		         (type "ext4")
		         (dependencies mapped-devices))
		       %base-file-systems))

  (users (cons (user-account
	        (name "guix")
	        (comment "guix")
	        (group "users")
	        (supplementary-groups '("wheel"))
	        (home-directory "/home/guix"))
	       %base-user-accounts))

  (sudoers-file
   (plain-file "sudoers" "\
root ALL=(ALL) ALL
%wheel ALL=(ALL) ALL
guix ALL=(ALL) NOPASSWD:ALL\n"))

  ;; Globally-installed packages.
  (packages (cons* tmux nss-certs gnutls wireguard-tools %base-packages))
  (services
   (cons*
    (service static-networking-service-type
	     (list (static-networking
		    (addresses (list (network-address
				      (device "enp3s0")
				      (value "@var{server-ip-address}/24"))))
		    (routes (list (network-route
				   (destination "default")
				   (gateway "@var{server-gateway}"))))
		    (name-servers '("213.186.33.99")))))

    (service unattended-upgrade-service-type)

    (service openssh-service-type
	     (openssh-configuration
	      (openssh openssh-sans-x)
	      (permit-root-login #f)
	      (authorized-keys
	       `(("guix" ,(plain-file "@var{ssh-key-name.pub}"
                                      "@var{ssh-public-key-content}"))))))
    (modify-services %base-services
      (sysctl-service-type
       config =>
       (sysctl-configuration
	(settings (append '(("net.ipv6.conf.all.autoconf" . "0")
			    ("net.ipv6.conf.all.accept_ra" . "0"))
			  %default-sysctl-settings))))))))
@end lisp

Don't forget to substitute the @var{server-ip-address},
@var{server-gateway}, @var{ssh-key-name} and
@var{ssh-public-key-content} variables with your own values.

The gateway is the last usable IP in your block so if you have a server
with an IP of @samp{37.187.79.10} then its gateway will be
@samp{37.187.79.254}.

Transfer your operating system declaration @file{os.scm} file on the
server via the @command{scp} or @command{sftp} commands.

Now all that is left is to install Guix with a @code{guix system init}
and restart.

However we first need to set up a chroot, because the root partition of
the rescue system is mounted on an aufs partition and if you try to
install Guix it will fail at the GRUB install step complaining about the
canonical path of "aufs".

Install packages that will be used in the chroot:

@example
guix install bash-static parted util-linux-with-udev coreutils guix
@end example

Then run the following to create directories needed for the chroot:

@example
cd /mnt && \
mkdir -p bin etc gnu/store root/.guix-profile/ root/.config/guix/current \
  var/guix proc sys dev
@end example

Copy the host resolv.conf in the chroot:

@example
cp /etc/resolv.conf etc/
@end example

Mount block devices, the store and its database and the current guix config:

@example
mount --rbind /proc /mnt/proc
mount --rbind /sys /mnt/sys
mount --rbind /dev /mnt/dev
mount --rbind /var/guix/ var/guix/
mount --rbind /gnu/store gnu/store/
mount --rbind /root/.config/ root/.config/
mount --rbind /root/.guix-profile/bin/ bin
mount --rbind /root/.guix-profile root/.guix-profile/
@end example

Chroot in /mnt and install the system:

@example
chroot /mnt/ /bin/bash

guix system init /root/os.scm /guix
@end example

Finally, from the web user interface (UI), change @samp{netboot} to
@samp{boot to disk} and restart (also from the web UI).

Wait a few minutes and try to ssh with @code{ssh
guix@@@var{server-ip-address>} -i @var{path-to-your-ssh-key}}

You should have a Guix system up and running on Kimsufi;
congratulations!

@node Setting up a bind mount
@section Setting up a bind mount

To bind mount a file system, one must first set up some definitions
before the @code{operating-system} section of the system definition.  In
this example we will bind mount a folder from a spinning disk drive to
@file{/tmp}, to save wear and tear on the primary SSD, without
dedicating an entire partition to be mounted as @file{/tmp}.

First, the source drive that hosts the folder we wish to bind mount
should be defined, so that the bind mount can depend on it.

@lisp
(define source-drive ;; "source-drive" can be named anything you want.
   (file-system
    (device (uuid "UUID goes here"))
    (mount-point "/path-to-spinning-disk-goes-here")
    (type "ext4"))) ;; Make sure to set this to the appropriate type for your drive.
@end lisp

The source folder must also be defined, so that guix will know it's not
a regular block device, but a folder.
@lisp
(define (%source-directory) "/path-to-spinning-disk-goes-here/tmp") ;; "source-directory" can be named any valid variable name.
@end lisp

Finally, inside the @code{file-systems} definition, we must add the
mount itself.

@lisp
(file-systems (cons*

                ...<other drives omitted for clarity>...

                source-drive ;; Must match the name you gave the source drive in the earlier definition.

                (file-system
                 (device (%source-directory)) ;; Make sure "source-directory" matches your earlier definition.
                 (mount-point "/tmp")
                 (type "none") ;; We are mounting a folder, not a partition, so this type needs to be "none"
                 (flags '(bind-mount))
                 (dependencies (list source-drive)) ;; Ensure "source-drive" matches what you've named the variable for the drive.
                 )

                 ...<other drives omitted for clarity>...

                ))
@end lisp

@node Getting substitutes from Tor
@section Getting substitutes from Tor

Guix daemon can use a HTTP proxy to get substitutes, here we are
configuring it to get them via Tor.

@quotation Warning
@emph{Not all} Guix daemon's traffic will go through Tor!  Only
HTTP/HTTPS will get proxied; FTP, Git protocol, SSH, etc connections
will still go through the clearnet.  Again, this configuration isn't
foolproof some of your traffic won't get routed by Tor at all.  Use it
at your own risk.

Also note that the procedure described here applies only to package
substitution. When you update your guix distribution with
@command{guix pull}, you still need to use @command{torsocks} if
you want to route the connection to guix's git repository servers
through Tor.
@end quotation

Guix's substitute server is available as a Onion service, if you want
to use it to get your substitutes through Tor configure your system as
follow:

@lisp
(use-modules (gnu))
(use-service-module base networking)

(operating-system
  …
  (services
    (cons
      (service tor-service-type
              (tor-configuration
                (config-file (plain-file "tor-config"
                                         "HTTPTunnelPort 127.0.0.1:9250"))))
      (modify-services %base-services
        (guix-service-type
          config => (guix-configuration
                      (inherit config)
                      ;; ci.guix.gnu.org's Onion service
                      (substitute-urls
                       "@value{SUBSTITUTE-TOR-URL}")
                      (http-proxy "http://localhost:9250")))))))
@end lisp

This will keep a tor process running that provides a HTTP CONNECT tunnel
which will be used by @command{guix-daemon}.  The daemon can use other
protocols than HTTP(S) to get remote resources, request using those
protocols won't go through Tor since we are only setting a HTTP tunnel
here.  Note that @code{substitutes-urls} is using HTTPS and not HTTP or
it won't work, that's a limitation of Tor's tunnel; you may want to use
@command{privoxy} instead to avoid such limitations.

If you don't want to always get substitutes through Tor but using it just
some of the times, then skip the @code{guix-configuration}.  When you
want to get a substitute from the Tor tunnel run:

@example
sudo herd set-http-proxy guix-daemon http://localhost:9250
guix build \
  --substitute-urls=@value{SUBSTITUTE-TOR-URL} @dots{}
@end example

@node Setting up NGINX with Lua
@section Setting up NGINX with Lua
@cindex nginx, lua, openresty, resty

NGINX could be extended with Lua scripts.

Guix provides NGINX service with ability to load Lua module and specific
Lua packages, and reply to requests by evaluating Lua scripts.

The following example demonstrates system definition with configuration
to evaluate @file{index.lua} Lua script on HTTP request to
@uref{http://localhost/hello} endpoint:

@example
local shell = require "resty.shell"

local stdin = ""
local timeout = 1000  -- ms
local max_size = 4096  -- byte

local ok, stdout, stderr, reason, status =
   shell.run([[/run/current-system/profile/bin/ls /tmp]], stdin, timeout, max_size)

ngx.say(stdout)
@end example

@lisp
(use-modules (gnu))
(use-service-modules #;… web)
(use-package-modules #;… lua)
(operating-system
  ;; …
  (services
   ;; …
   (service nginx-service-type
            (nginx-configuration
             (modules
              (list
               (file-append nginx-lua-module "/etc/nginx/modules/ngx_http_lua_module.so")))
             (lua-package-path (list lua-resty-core
                                     lua-resty-lrucache
                                     lua-resty-signal
                                     lua-tablepool
                                     lua-resty-shell))
             (lua-package-cpath (list lua-resty-signal))
             (server-blocks
              (list (nginx-server-configuration
                     (server-name '("localhost"))
                     (listen '("80"))
                     (root "/etc")
                     (locations (list
                                 (nginx-location-configuration
                                  (uri "/hello")
                                  (body (list #~(format #f "content_by_lua_file ~s;"
                                                        #$(local-file "index.lua"))))))))))))))
@end lisp

@node Music Server with Bluetooth Audio
@section Music Server with Bluetooth Audio
@cindex mpd
@cindex music server, headless
@cindex bluetooth, ALSA configuration

MPD, the Music Player Daemon, is a flexible server-side application for
playing music.  Client programs on different machines on the network ---
a mobile phone, a laptop, a desktop workstation --- can connect to it to
control the playback of audio files from your local music collection.
MPD decodes the audio files and plays them back on one or many outputs.

By default MPD will play to the default audio device.  In the example
below we make things a little more interesting by setting up a headless
music server.  There will be no graphical user interface, no Pulseaudio
daemon, and no local audio output.  Instead we will configure MPD with
two outputs: a bluetooth speaker and a web server to serve audio streams
to any streaming media player.

Bluetooth is often rather frustrating to set up.  You will have to pair
your Bluetooth device and make sure that the device is automatically
connected as soon as it powers on.  The Bluetooth system service
returned by the @code{bluetooth-service} procedure provides the
infrastructure needed to set this up.

Reconfigure your system with at least the following services and
packages:

@lisp
(operating-system
  ;; …
  (packages (cons* bluez bluez-alsa
                   %base-packages))
  (services
   ;; …
   (dbus-service #:services (list bluez-alsa))
   (bluetooth-service #:auto-enable? #t)))
@end lisp

Start the @code{bluetooth} service and then use @command{bluetoothctl}
to scan for Bluetooth devices.  Try to identify your Bluetooth speaker
and pick out its device ID from the resulting list of devices that is
indubitably dominated by a baffling smorgasbord of your neighbors' home
automation gizmos.  This only needs to be done once:

@example
$ bluetoothctl 
[NEW] Controller 00:11:22:33:95:7F BlueZ 5.40 [default]

[bluetooth]# power on
[bluetooth]# Changing power on succeeded

[bluetooth]# agent on
[bluetooth]# Agent registered

[bluetooth]# default-agent
[bluetooth]# Default agent request successful

[bluetooth]# scan on
[bluetooth]# Discovery started
[CHG] Controller 00:11:22:33:95:7F Discovering: yes
[NEW] Device AA:BB:CC:A4:AA:CD My Bluetooth Speaker
[NEW] Device 44:44:FF:2A:20:DC My Neighbor's TV
@dots{}

[bluetooth]# pair AA:BB:CC:A4:AA:CD
Attempting to pair with AA:BB:CC:A4:AA:CD
[CHG] Device AA:BB:CC:A4:AA:CD Connected: yes

[My Bluetooth Speaker]# [CHG] Device AA:BB:CC:A4:AA:CD UUIDs: 0000110b-0000-1000-8000-00xxxxxxxxxx
[CHG] Device AA:BB:CC:A4:AA:CD UUIDs: 0000110c-0000-1000-8000-00xxxxxxxxxx
[CHG] Device AA:BB:CC:A4:AA:CD UUIDs: 0000110e-0000-1000-8000-00xxxxxxxxxx
[CHG] Device AA:BB:CC:A4:AA:CD Paired: yes
Pairing successful

[CHG] Device AA:BB:CC:A4:AA:CD Connected: no

[bluetooth]# 
[bluetooth]# trust AA:BB:CC:A4:AA:CD
[bluetooth]# [CHG] Device AA:BB:CC:A4:AA:CD Trusted: yes
Changing AA:BB:CC:A4:AA:CD trust succeeded

[bluetooth]# 
[bluetooth]# connect AA:BB:CC:A4:AA:CD
Attempting to connect to AA:BB:CC:A4:AA:CD
[bluetooth]# [CHG] Device AA:BB:CC:A4:AA:CD RSSI: -63
[CHG] Device AA:BB:CC:A4:AA:CD Connected: yes
Connection successful

[My Bluetooth Speaker]# scan off
[CHG] Device AA:BB:CC:A4:AA:CD RSSI is nil
Discovery stopped
[CHG] Controller 00:11:22:33:95:7F Discovering: no
@end example

Congratulations, you can now automatically connect to your Bluetooth
speaker!

It is now time to configure ALSA to use the @emph{bluealsa} Bluetooth
module, so that you can define an ALSA pcm device corresponding to your
Bluetooth speaker.  For a headless server using @emph{bluealsa} with a
fixed Bluetooth device is likely simpler than configuring Pulseaudio and
its stream switching behavior.  We configure ALSA by crafting a custom
@code{alsa-configuration} for the @code{alsa-service-type}.  The
configuration will declare a @code{pcm} type @code{bluealsa} from the
@code{bluealsa} module provided by the @code{bluez-alsa} package, and
then define a @code{pcm} device of that type for your Bluetooth speaker.

All that is left then is to make MPD send audio data to this ALSA
device.  We also add a secondary MPD output that makes the currently
played audio files available as a stream through a web server on port
8080.  When enabled a device on the network could listen to the audio
stream by connecting any capable media player to the HTTP server on port
8080, independent of the status of the Bluetooth speaker.

What follows is the outline of an @code{operating-system} declaration
that should accomplish the above-mentioned tasks:

@lisp
(use-modules (gnu))
(use-service-modules audio dbus sound #;… etc)
(use-package-modules audio linux #;… etc)
(operating-system
  ;; …
  (packages (cons* bluez bluez-alsa
                   %base-packages))
  (services
   ;; …
   (service mpd-service-type
            (mpd-configuration
             (user "your-username")
             (music-dir "/path/to/your/music")
             (address "192.168.178.20")
             (outputs (list (mpd-output
                             (type "alsa")
                             (name "MPD")
                             (extra-options
                              ;; Use the same name as in the ALSA
                              ;; configuration below.
                              '((device . "pcm.btspeaker"))))
                            (mpd-output
                             (type "httpd")
                             (name "streaming")
                             (enabled? #false)
                             (always-on? #true)
                             (tags? #true)
                             (mixer-type 'null)
                             (extra-options
                              '((encoder . "vorbis")
                                (port    . "8080")
                                (bind-to-address . "192.168.178.20")
                                (max-clients . "0") ;no limit
                                (quality . "5.0")
                                (format  . "44100:16:1"))))))))
   (dbus-service #:services (list bluez-alsa))
   (bluetooth-service #:auto-enable? #t)
   (service alsa-service-type
            (alsa-configuration
             (pulseaudio? #false) ;we don't need it
             (extra-options
              #~(string-append "\
# Declare Bluetooth audio device type \"bluealsa\" from bluealsa module
pcm_type.bluealsa @{
    lib \"" #$(file-append bluez-alsa "/lib/alsa-lib/libasound_module_pcm_bluealsa.so") "\"
@}

# Declare control device type \"bluealsa\" from the same module
ctl_type.bluealsa @{
    lib \"" #$(file-append bluez-alsa "/lib/alsa-lib/libasound_module_ctl_bluealsa.so") "\"
@}

# Define the actual Bluetooth audio device.
pcm.btspeaker @{
    type bluealsa
    device \"AA:BB:CC:A4:AA:CD\" # unique device identifier
    profile \"a2dp\"
@}

# Define an associated controller.
ctl.btspeaker @{
    type bluealsa
@}
"))))))
@end lisp

Enjoy the music with the MPD client of your choice or a media player
capable of streaming via HTTP!


@c *********************************************************************
@node Containers
@chapter Containers

The kernel Linux provides a number of shared facilities that are
available to processes in the system.  These facilities include a shared
view on the file system, other processes, network devices, user and
group identities, and a few others.  Since Linux 3.19 a user can choose
to @emph{unshare} some of these shared facilities for selected
processes, providing them (and their child processes) with a different
view on the system.

A process with an unshared @code{mount} namespace, for example, has its
own view on the file system --- it will only be able to see directories
that have been explicitly bound in its mount namespace.  A process with
its own @code{proc} namespace will consider itself to be the only
process running on the system, running as PID 1.

Guix uses these kernel features to provide fully isolated environments
and even complete Guix System containers, lightweight virtual machines
that share the host system's kernel.  This feature comes in especially
handy when using Guix on a foreign distribution to prevent interference
from foreign libraries or configuration files that are available
system-wide.

@menu
* Guix Containers::             Perfectly isolated environments
* Guix System Containers::      A system inside your system
@end menu

@node Guix Containers
@section Guix Containers

The easiest way to get started is to use @command{guix shell} with the
@option{--container} option.  @xref{Invoking guix shell,,, guix, GNU
Guix Reference Manual} for a reference of valid options.

The following snippet spawns a minimal shell process with most
namespaces unshared from the system.  The current working directory is
visible to the process, but anything else on the file system is
unavailable.  This extreme isolation can be very useful when you want to
rule out any sort of interference from environment variables, globally
installed libraries, or configuration files.

@example
guix shell --container
@end example

It is a bleak environment, barren, desolate.  You will find that not
even the GNU coreutils are available here, so to explore this deserted
wasteland you need to use built-in shell commands.  Even the usually
gigantic @file{/gnu/store} directory is reduced to a faint shadow of
itself.

@example sh
$ echo /gnu/store/*
/gnu/store/@dots{}-gcc-10.3.0-lib
/gnu/store/@dots{}-glibc-2.33
/gnu/store/@dots{}-bash-static-5.1.8
/gnu/store/@dots{}-ncurses-6.2.20210619
/gnu/store/@dots{}-bash-5.1.8
/gnu/store/@dots{}-profile
/gnu/store/@dots{}-readline-8.1.1
@end example

@cindex exiting a container
There isn't much you can do in an environment like this other than
exiting it.  You can use @key{^D} or @command{exit} to terminate this
limited shell environment.

@cindex exposing directories, container
@cindex sharing directories, container
@cindex mapping locations, container
You can make other directories available inside of the container
environment; use @option{--expose=DIRECTORY} to bind-mount the given
directory as a read-only location inside the container, or use
@option{--share=DIRECTORY} to make the location writable.  With an
additional mapping argument after the directory name you can control the
name of the directory inside the container.  In the following example we
map @file{/etc} on the host system to @file{/the/host/etc} inside a
container in which the GNU coreutils are installed.

@example sh
$ guix shell --container --share=/etc=/the/host/etc coreutils
$ ls /the/host/etc
@end example

Similarly, you can prevent the current working directory from being
mapped into the container with the @option{--no-cwd} option.  Another
good idea is to create a dedicated directory that will serve as the
container's home directory, and spawn the container shell from that
directory.

@cindex hide system libraries, container
@cindex avoid ABI mismatch, container
On a foreign system a container environment can be used to compile
software that cannot possibly be linked with system libraries or with
the system's compiler toolchain.  A common use-case in a research
context is to install packages from within an R session.  Outside of a
container environment there is a good chance that the foreign compiler
toolchain and incompatible system libraries are found first, resulting
in incompatible binaries that cannot be used by R.  In a container shell
this problem disappears, as system libraries and executables simply
aren't available due to the unshared @code{mount} namespace.

Let's take a comprehensive manifest providing a comfortable development
environment for use with R:

@lisp
(specifications->manifest
  (list "r-minimal"

        ;; base packages
        "bash-minimal"
        "glibc-locales"
        "nss-certs"

        ;; Common command line tools lest the container is too empty.
        "coreutils"
        "grep"
        "which"
        "wget"
        "sed"

        ;; R markdown tools
        "pandoc"

        ;; Toolchain and common libraries for "install.packages"
        "gcc-toolchain@@10"
        "gfortran-toolchain"
        "gawk"
        "tar"
        "gzip"
        "unzip"
        "make"
        "cmake"
        "pkg-config"
        "cairo"
        "libxt"
        "openssl"
        "curl"
        "zlib"))
@end lisp

Let's use this to run R inside a container environment.  For convenience
we share the @code{net} namespace to use the host system's network
interfaces.  Now we can build R packages from source the traditional way
without having to worry about ABI mismatch or incompatibilities.

@example sh
$ guix shell --container --network --manifest=manifest.scm -- R

R version 4.2.1 (2022-06-23) -- "Funny-Looking Kid"
Copyright (C) 2022 The R Foundation for Statistical Computing
@dots{}
> e <- Sys.getenv("GUIX_ENVIRONMENT")
> Sys.setenv(GIT_SSL_CAINFO=paste0(e, "/etc/ssl/certs/ca-certificates.crt"))
> Sys.setenv(SSL_CERT_FILE=paste0(e, "/etc/ssl/certs/ca-certificates.crt"))
> Sys.setenv(SSL_CERT_DIR=paste0(e, "/etc/ssl/certs"))
> install.packages("Cairo", lib=paste0(getwd()))
@dots{}
* installing *source* package 'Cairo' ...
@dots{}
* DONE (Cairo)

The downloaded source packages are in
	'/tmp/RtmpCuwdwM/downloaded_packages'
> library("Cairo", lib=getwd())
> # success!
@end example

Using container shells is fun, but they can become a little cumbersome
when you want to go beyond just a single interactive process.  Some
tasks become a lot easier when they sit on the rock solid foundation of
a proper Guix System and its rich set of system services.  The next
section shows you how to launch a complete Guix System inside of a
container.


@node Guix System Containers
@section Guix System Containers

The Guix System provides a wide array of interconnected system services
that are configured declaratively to form a dependable stateless GNU
System foundation for whatever tasks you throw at it.  Even when using
Guix on a foreign distribution you can benefit from the design of Guix
System by running a system instance as a container.  Using the same
kernel features of unshared namespaces mentioned in the previous
section, the resulting Guix System instance is isolated from the host
system and only shares file system locations that you explicitly
declare.

A Guix System container differs from the shell process created by
@command{guix shell --container} in a number of important ways.  While
in a container shell the containerized process is a Bash shell process,
a Guix System container runs the Shepherd as PID 1.  In a system
container all system services (@pxref{Services,,, guix, GNU Guix
Reference Manual}) are set up just as they would be on a Guix System in
a virtual machine or on bare metal---this includes daemons managed by
the GNU@tie{}Shepherd (@pxref{Shepherd Services,,, guix, GNU Guix
Reference Manual}) as well as other kinds of extensions to the operating
system (@pxref{Service Composition,,, guix, GNU Guix Reference Manual}).

The perceived increase in complexity of running a Guix System container
is easily justified when dealing with more complex applications that
have higher or just more rigid requirements on their execution
contexts---configuration files, dedicated user accounts, directories for
caches or log files, etc.  In Guix System the demands of this kind of
software are satisfied through the deployment of system services.


@menu
* A Database Container::
* Container Networking::
@end menu

@node A Database Container
@subsection A Database Container

A good example might be a PostgreSQL database server.  Much of the
complexity of setting up such a database server is encapsulated in this
deceptively short service declaration:

@lisp
(service postgresql-service-type
         (postgresql-configuration
          (postgresql postgresql-14)))
@end lisp

A complete operating system declaration for use with a Guix System
container would look something like this:

@lisp
(use-modules (gnu))
(use-package-modules databases)
(use-service-modules databases)

(operating-system
  (host-name "container")
  (timezone "Europe/Berlin")
  (file-systems (cons (file-system
                        (device (file-system-label "does-not-matter"))
                        (mount-point "/")
                        (type "ext4"))
                      %base-file-systems))
  (bootloader (bootloader-configuration
               (bootloader grub-bootloader)
               (targets '("/dev/sdX"))))
  (services
   (cons* (service postgresql-service-type
                   (postgresql-configuration
                    (postgresql postgresql-14)
                    (config-file
                     (postgresql-config-file
                      (log-destination "stderr")
                      (hba-file
                       (plain-file "pg_hba.conf"
                                   "\
local	all	all			trust
host	all	all	10.0.0.1/32 	trust"))
                      (extra-config
                       '(("listen_addresses" "*")
                         ("log_directory"    "/var/log/postgresql")))))))
          (service postgresql-role-service-type
                   (postgresql-role-configuration
                    (roles
                     (list (postgresql-role
                            (name "test")
                            (create-database? #t))))))
          %base-services)))
@end lisp

With @code{postgresql-role-service-type} we define a role ``test'' and
create a matching database, so that we can test right away without any
further manual setup.  The @code{postgresql-config-file} settings allow
a client from IP address 10.0.0.1 to connect without requiring
authentication---a bad idea in production systems, but convenient for
this example.

Let's build a script that will launch an instance of this Guix System as
a container.  Write the @code{operating-system} declaration above to a
file @file{os.scm} and then use @command{guix system container} to build
the launcher.  (@pxref{Invoking guix system,,, guix, GNU Guix Reference
Manual}).

@example
$ guix system container os.scm
The following derivations will be built:
  /gnu/store/@dots{}-run-container.drv
  @dots{}
building /gnu/store/@dots{}-run-container.drv...
/gnu/store/@dots{}-run-container
@end example

Now that we have a launcher script we can run it to spawn the new system
with a running PostgreSQL service.  Note that due to some as yet
unresolved limitations we need to run the launcher as the root user, for
example with @command{sudo}.

@example
$ sudo /gnu/store/@dots{}-run-container
system container is running as PID 5983
@dots{}
@end example

Background the process with @key{Ctrl-z} followed by @command{bg}.  Note
the process ID in the output; we will need it to connect to the
container later.  You know what?  Let's try attaching to the container
right now.  We will use @command{nsenter}, a tool provided by the
@code{util-linux} package:

@example
$ guix shell util-linux
$ sudo nsenter -a -t 5983
root@@container /# pgrep -a postgres
49 /gnu/store/@dots{}-postgresql-14.4/bin/postgres -D /var/lib/postgresql/data --config-file=/gnu/store/@dots{}-postgresql.conf -p 5432
51 postgres: checkpointer
52 postgres: background writer
53 postgres: walwriter
54 postgres: autovacuum launcher
55 postgres: stats collector
56 postgres: logical replication launcher
root@@container /# exit
@end example

The PostgreSQL service is running in the container!


@node Container Networking
@subsection Container Networking
@cindex container networking

What good is a Guix System running a PostgreSQL database service as a
container when we can only talk to it with processes originating in the
container?  It would be much better if we could talk to the database
over the network.

The easiest way to do this is to create a pair of connected virtual
Ethernet devices (known as @code{veth}).  We move one of the devices
(@code{ceth-test}) into the @code{net} namespace of the container and
leave the other end (@code{veth-test}) of the connection on the host
system.

@example
pid=5983
ns="guix-test"
host="veth-test"
client="ceth-test"

# Attach the new net namespace "guix-test" to the container PID.
sudo ip netns attach $ns $pid

# Create the pair of devices
sudo ip link add $host type veth peer name $client

# Move the client device into the container's net namespace
sudo ip link set $client netns $ns
@end example

Then we configure the host side:

@example
sudo ip link set $host up
sudo ip addr add 10.0.0.1/24 dev $host
@end example

@dots{}and then we configure the client side:

@example
sudo ip netns exec $ns  ip link set lo up
sudo ip netns exec $ns  ip link set $client up
sudo ip netns exec $ns  ip addr add 10.0.0.2/24 dev $client
@end example

At this point the host can reach the container at IP address 10.0.0.2,
and the container can reach the host at IP 10.0.0.1.  This is all we
need to talk to the database server inside the container from the host
system on the outside.

@example
$ psql -h 10.0.0.2 -U test
psql (14.4)
Type "help" for help.

test=> CREATE TABLE hello (who TEXT NOT NULL);
CREATE TABLE
test=> INSERT INTO hello (who) VALUES ('world');
INSERT 0 1
test=> SELECT * FROM hello;
  who
-------
 world
(1 row)
@end example

Now that we're done with this little demonstration let's clean up:

@example
sudo kill $pid
sudo ip netns del $ns
sudo ip link del $host
@end example

@c *********************************************************************
@node Virtual Machines
@chapter Virtual Machines

Guix can produce disk images (@pxref{Invoking guix system,,, guix, GNU
Guix Reference Manual}) that can be used with virtual machines solutions
such as virt-manager, GNOME Boxes or the more bare QEMU, among others.

This chapter aims to provide hands-on, practical examples that relates
to the usage and configuration of virtual machines on a Guix System.

@menu
* Network bridge for QEMU::
* Routed network for libvirt::
@end menu

@node Network bridge for QEMU
@section Network bridge for QEMU
@cindex Network bridge interface
@cindex networking, bridge
@cindex qemu, network bridge

By default, QEMU uses a so-called ``user mode'' host network back-end,
which is convenient as it does not require any configuration.
Unfortunately, it is also quite limited.  In this mode, the guest
@abbr{VM, virtual machine} can access the network the same way the host
would, but it cannot be reached from the host.  Additionally, since the
QEMU user networking mode relies on ICMP, ICMP-based networking tools
such as @command{ping} do @emph{not} work in this mode.  Thus, it is
often desirable to configure a network bridge, which enables the guest
to fully participate in the network.  This is necessary, for example,
when the guest is to be used as a server.

@subsection Creating a network bridge interface

There are many ways to create a network bridge.  The following command
shows how to use NetworkManager and its @command{nmcli} command line
interface (CLI) tool, which should already be available if your
operating system declaration is based on one of the desktop templates:

@example sh
# nmcli con add type bridge con-name br0 ifname br0
@end example

To have this bridge be part of your network, you must associate your
network bridge with the Ethernet interface used to connect with the
network.  Assuming your interface is named @samp{enp2s0}, the following
command can be used to do so:

@example sh
# nmcli con add type bridge-slave ifname enp2s0 master br0
@end example

@quotation Important
Only Ethernet interfaces can be added to a bridge.  For wireless
interfaces, consider the routed network approach detailed in
@xref{Routed network for libvirt}.
@end quotation

By default, the network bridge will allow your guests to obtain their IP
address via DHCP, if available on your local network.  For simplicity,
this is what we will use here.  To easily find the guests, they can be
configured to advertise their host names via mDNS.

@subsection Configuring the QEMU bridge helper script

QEMU comes with a helper program to conveniently make use of a network
bridge interface as an unprivileged user @pxref{Network options,,, QEMU,
QEMU Documentation}.  The binary must be made setuid root for proper
operation; this can be achieved by adding it to the
@code{setuid-programs} field of your (host) @code{operating-system}
definition, as shown below:

@example lisp
(setuid-programs
 (cons (file-append qemu "/libexec/qemu-bridge-helper")
       %setuid-programs))
@end example

The file @file{/etc/qemu/bridge.conf} must also be made to allow the
bridge interface, as the default is to deny all.  Add the following to
your list of services to do so:

@example lisp
(extra-special-file "/etc/qemu/host.conf" "allow br0\n")
@end example

@subsection Invoking QEMU with the right command line options

When invoking QEMU, the following options should be provided so that the
network bridge is used, after having selected a unique MAC address for
the guest.

@quotation Important
By default, a single MAC address is used for all guests, unless
provided.  Failing to provided different MAC addresses to each virtual
machine making use of the bridge would cause networking issues.
@end quotation

@example sh
$ qemu-system-x86_64 [...] \
    -device virtio-net-pci,netdev=user0,mac=XX:XX:XX:XX:XX:XX \
    -netdev bridge,id=user0,br=br0 \
    [...]
@end example

To generate MAC addresses that have the QEMU registered prefix, the
following snippet can be employed:

@example sh
mac_address="52:54:00:$(dd if=/dev/urandom bs=512 count=1 2>/dev/null \
                           | md5sum \
                           | sed -E 's/^(..)(..)(..).*$/\1:\2:\3/')"
echo $mac_address
@end example

@subsection Networking issues caused by Docker

If you use Docker on your machine, you may experience connectivity
issues when attempting to use a network bridge, which are caused by
Docker also relying on network bridges and configuring its own routing
rules.  The solution is add the following @code{iptables} snippet to
your @code{operating-system} declaration:

@example lisp
(service iptables-service-type
             (iptables-configuration
              (ipv4-rules (plain-file "iptables.rules" "\
*filter
:INPUT ACCEPT [0:0]
:FORWARD DROP [0:0]
:OUTPUT ACCEPT [0:0]
-A FORWARD -i br0 -o br0 -j ACCEPT
COMMIT
"))
@end example

@node Routed network for libvirt
@section Routed network for libvirt
@cindex Virtual network bridge interface
@cindex networking, virtual bridge
@cindex libvirt, virtual network bridge

If the machine hosting your virtual machines is connected wirelessly to
the network, you won't be able to use a true network bridge as explained
in the preceding section (@pxref{Network bridge for QEMU}).  In this
case, the next best option is to use a @emph{virtual} bridge with static
routing and to configure a libvirt-powered virtual machine to use it
(via the @command{virt-manager} GUI for example).  This is similar to
the default mode of operation of QEMU/libvirt, except that instead of
using @abbr{NAT, Network Address Translation}, it relies on static
routes to join the @abbr{VM, virtual machine} IP address to the
@abbr{LAN, local area network}.  This provides two-way connectivity to
and from the virtual machine, which is needed for exposing services
hosted on the virtual machine.

@subsection Creating a virtual network bridge

A virtual network bridge consists of a few components/configurations,
such as a @abbr{TUN, network tunnel} interface, DHCP server (dnsmasq)
and firewall rules (iptables).  The @command{virsh} command, provided by
the @code{libvirt} package, makes it very easy to create a virtual
bridge.  You first need to choose a network subnet for your virtual
bridge; if your home LAN is in the @samp{192.168.1.0/24} network, you
could opt to use e.g.@: @samp{192.168.2.0/24}.  Define an XML file,
e.g.@: @file{/tmp/virbr0.xml}, containing the following:

@example
<network>
  <name>virbr0</name>
  <bridge name="virbr0" />
  <forward mode="route"/>
  <ip address="192.168.2.0" netmask="255.255.255.0">
    <dhcp>
      <range start="192.168.2.1" end="192.168.2.254"/>
    </dhcp>
  </ip>
</network>
@end example

Then create and configure the interface using the @command{virsh}
command, as root:

@example
virsh net-define /tmp/virbr0.xml
virsh net-autostart virbr0
virsh net-start virbr0
@end example

The @samp{virbr0} interface should now be visible e.g.@: via the
@samp{ip address} command.  It will be automatically started every time
your libvirt virtual machine is started.

@subsection Configuring the static routes for your virtual bridge

If you configured your virtual machine to use your newly created
@samp{virbr0} virtual bridge interface, it should already receive an IP
via DHCP such as @samp{192.168.2.15} and be reachable from the server
hosting it, e.g.@: via @samp{ping 192.168.2.15}.  There's one last
configuration needed so that the VM can reach the external network:
adding static routes to the network's router.

In this example, the LAN network is @samp{192.168.1.0/24} and the router
configuration web page may be accessible via e.g.@: the
@url{http://192.168.1.1} page.  On a router running the
@url{https://librecmc.org/, libreCMC} firmware, you would navigate to
the @clicksequence{Network @click{} Static Routes} page
(@url{https://192.168.1.1/cgi-bin/luci/admin/network/routes}), and you
would add a new entry to the @samp{Static IPv4 Routes} with the
following information:

@table @samp
@item Interface
lan
@item Target
192.168.2.0
@item IPv4-Netmask
255.255.255.0
@item IPv4-Gateway
@var{server-ip}
@item Route type
unicast
@end table

where @var{server-ip} is the IP address of the machine hosting the VMs,
which should be static.

After saving/applying this new static route, external connectivity
should work from within your VM; you can e.g.@: run @samp{ping gnu.org}
to verify that it functions correctly.

@c *********************************************************************
@node Advanced package management
@chapter Advanced package management

Guix is a functional package manager that offers many features beyond
what more traditional package managers can do.  To the uninitiated,
those features might not have obvious use cases at first.  The purpose
of this chapter is to demonstrate some advanced package management
concepts.

@pxref{Package Management,,, guix, GNU Guix Reference Manual} for a complete
reference.

@menu
* Guix Profiles in Practice::   Strategies for multiple profiles and manifests.
@end menu

@node Guix Profiles in Practice
@section Guix Profiles in Practice

Guix provides a very useful feature that may be quite foreign to newcomers:
@dfn{profiles}.  They are a way to group package installations together and all users
on the same system are free to use as many profiles as they want.

Whether you're a developer or not, you may find that multiple profiles bring you
great power and flexibility.  While they shift the paradigm somewhat compared to
@emph{traditional package managers}, they are very convenient to use once you've
understood how to set them up.

@quotation Note
This section is an opinionated guide on the use of multiple profiles.
It predates @command{guix shell} and its fast profile cache
(@pxref{Invoking guix shell,,, guix, GNU Guix Reference Manual}).

In many cases, you may find that using @command{guix shell} to set up
the environment you need, when you need it, is less work that
maintaining a dedicated profile.  Your call!
@end quotation

If you are familiar with Python's @samp{virtualenv}, you can think of a profile as a
kind of universal @samp{virtualenv} that can hold any kind of software whatsoever, not
just Python software.  Furthermore, profiles are self-sufficient: they capture
all the runtime dependencies which guarantees that all programs within a profile
will always work at any point in time.

Multiple profiles have many benefits:

@itemize
@item
Clean semantic separation of the various packages a user needs for different contexts.

@item
Multiple profiles can be made available into the environment either on login
or within a dedicated shell.

@item
Profiles can be loaded on demand.  For instance, the user can use multiple
shells, each of them running different profiles.

@item
Isolation: Programs from one profile will not use programs from the other, and
the user can even install different versions of the same programs to the two
profiles without conflict.

@item
Deduplication: Profiles share dependencies that happens to be the exact same.
This makes multiple profiles storage-efficient.

@item
Reproducible: when used with declarative manifests, a profile can be fully
specified by the Guix commit that was active when it was set up.  This means
that the exact same profile can be
@uref{https://guix.gnu.org/blog/2018/multi-dimensional-transactions-and-rollbacks-oh-my/,
set up anywhere and anytime}, with just the commit information.  See the
section on @ref{Reproducible profiles}.

@item
Easier upgrades and maintenance: Multiple profiles make it easy to keep
package listings at hand and make upgrades completely frictionless.
@end itemize

Concretely, here follows some typical profiles:

@itemize
@item
The dependencies of a project you are working on.

@item
Your favourite programming language libraries.

@item
Laptop-specific programs (like @samp{powertop}) that you don't need on a desktop.

@item
@TeX{}live (this one can be really useful when you need to install just one
package for this one document you've just received over email).

@item
Games.
@end itemize

Let's dive in the set up!

@menu
* Basic setup with manifests::
* Required packages::
* Default profile::
* The benefits of manifests::
* Reproducible profiles::
@end menu

@node Basic setup with manifests
@subsection Basic setup with manifests

A Guix profile can be set up @i{via} a @dfn{manifest}.  A manifest is a
snippet of Scheme code that specifies the set of packages you want to
have in your profile; it looks like this:

@lisp
(specifications->manifest
  '("package-1"
    ;; Version 1.3 of package-2.
    "package-2@@1.3"
    ;; The "lib" output of package-3.
    "package-3:lib"
    ; ...
    "package-N"))
@end lisp

@xref{Writing Manifests,,, guix, GNU Guix Reference Manual}, for
more information about the syntax.

We can create a manifest specification per profile and install them this way:

@example
GUIX_EXTRA_PROFILES=$HOME/.guix-extra-profiles
mkdir -p "$GUIX_EXTRA_PROFILES"/my-project # if it does not exist yet
guix package --manifest=/path/to/guix-my-project-manifest.scm --profile="$GUIX_EXTRA_PROFILES"/my-project/my-project
@end example

Here we set an arbitrary variable @samp{GUIX_EXTRA_PROFILES} to point to the directory
where we will store our profiles in the rest of this article.

Placing all your profiles in a single directory, with each profile getting its
own sub-directory, is somewhat cleaner.  This way, each sub-directory will
contain all the symlinks for precisely one profile.  Besides, ``looping over
profiles'' becomes obvious from any programming language (e.g.@: a shell script) by
simply looping over the sub-directories of @samp{$GUIX_EXTRA_PROFILES}.

Note that it's also possible to loop over the output of

@example
guix package --list-profiles
@end example

although you'll probably have to filter out @file{~/.config/guix/current}.

To enable all profiles on login, add this to your @file{~/.bash_profile} (or similar):

@example
for i in $GUIX_EXTRA_PROFILES/*; do
  profile=$i/$(basename "$i")
  if [ -f "$profile"/etc/profile ]; then
    GUIX_PROFILE="$profile"
    . "$GUIX_PROFILE"/etc/profile
  fi
  unset profile
done
@end example

Note to Guix System users: the above reflects how your default profile
@file{~/.guix-profile} is activated from @file{/etc/profile}, that latter being loaded by
@file{~/.bashrc} by default.

You can obviously choose to only enable a subset of them:

@example
for i in "$GUIX_EXTRA_PROFILES"/my-project-1 "$GUIX_EXTRA_PROFILES"/my-project-2; do
  profile=$i/$(basename "$i")
  if [ -f "$profile"/etc/profile ]; then
    GUIX_PROFILE="$profile"
    . "$GUIX_PROFILE"/etc/profile
  fi
  unset profile
done
@end example

When a profile is off, it's straightforward to enable it for an individual shell
without "polluting" the rest of the user session:

@example
GUIX_PROFILE="path/to/my-project" ; . "$GUIX_PROFILE"/etc/profile
@end example

The key to enabling a profile is to @emph{source} its @samp{etc/profile} file.  This file
contains shell code that exports the right environment variables necessary to
activate the software contained in the profile.  It is built automatically by
Guix and meant to be sourced.
It contains the same variables you would get if you ran:

@example
guix package --search-paths=prefix --profile=$my_profile"
@end example

Once again, see (@pxref{Invoking guix package,,, guix, GNU Guix Reference Manual})
for the command line options.

To upgrade a profile, simply install the manifest again:

@example
guix package -m /path/to/guix-my-project-manifest.scm -p "$GUIX_EXTRA_PROFILES"/my-project/my-project
@end example

To upgrade all profiles, it's easy enough to loop over them.  For instance,
assuming your manifest specifications are stored in
@file{~/.guix-manifests/guix-$profile-manifest.scm}, with @samp{$profile} being the name
of the profile (e.g.@: "project1"), you could do the following in Bourne shell:

@example
for profile in "$GUIX_EXTRA_PROFILES"/*; do
  guix package --profile="$profile" --manifest="$HOME/.guix-manifests/guix-$profile-manifest.scm"
done
@end example

Each profile has its own generations:

@example
guix package -p "$GUIX_EXTRA_PROFILES"/my-project/my-project --list-generations
@end example

You can roll-back to any generation of a given profile:

@example
guix package -p "$GUIX_EXTRA_PROFILES"/my-project/my-project --switch-generations=17
@end example

Finally, if you want to switch to a profile without inheriting from the
current environment, you can activate it from an empty shell:

@example
env -i $(which bash) --login --noprofile --norc
. my-project/etc/profile
@end example

@node Required packages
@subsection Required packages

Activating a profile essentially boils down to exporting a bunch of
environmental variables.  This is the role of the @samp{etc/profile} within the
profile.

@emph{Note: Only the environmental variables of the packages that consume them will
be set.}

For instance, @samp{MANPATH} won't be set if there is no consumer application for man
pages within the profile.  So if you need to transparently access man pages once
the profile is loaded, you've got two options:

@itemize
@item
Either export the variable manually, e.g.
@example
export MANPATH=/path/to/profile$@{MANPATH:+:@}$MANPATH
@end example

@item
Or include @samp{man-db} to the profile manifest.
@end itemize

The same is true for @samp{INFOPATH} (you can install @samp{info-reader}),
@samp{PKG_CONFIG_PATH} (install @samp{pkg-config}), etc.

@node Default profile
@subsection Default profile

What about the default profile that Guix keeps in @file{~/.guix-profile}?

You can assign it the role you want.  Typically you would install the manifest
of the packages you want to use all the time.

Alternatively, you could keep it ``manifest-less'' for throw-away packages
that you would just use for a couple of days.
This way makes it convenient to run

@example
guix install package-foo
guix upgrade package-bar
@end example

without having to specify the path to a profile.

@node The benefits of manifests
@subsection The benefits of manifests

Manifests let you @dfn{declare} the set of packages you'd like to have
in a profile (@pxref{Writing Manifests,,, guix, GNU Guix Reference Manual}).
They are a convenient way to keep your package lists around and, say,
to synchronize them across multiple machines using a version control system.

A common complaint about manifests is that they can be slow to install when they
contain large number of packages.  This is especially cumbersome when you just
want get an upgrade for one package within a big manifest.

This is one more reason to use multiple profiles, which happen to be just
perfect to break down manifests into multiple sets of semantically connected
packages.  Using multiple, small profiles provides more flexibility and
usability.

Manifests come with multiple benefits.  In particular, they ease maintenance:

@itemize
@item
When a profile is set up from a manifest, the manifest itself is
self-sufficient to keep a ``package listing'' around and reinstall the profile
later or on a different system.  For ad-hoc profiles, we would need to
generate a manifest specification manually and maintain the package versions
for the packages that don't use the default version.

@item
@code{guix package --upgrade} always tries to update the packages that have
propagated inputs, even if there is nothing to do.  Guix manifests remove this
problem.

@item
When partially upgrading a profile, conflicts may arise (due to diverging
dependencies between the updated and the non-updated packages) and they can be
annoying to resolve manually.  Manifests remove this problem altogether since
all packages are always upgraded at once.

@item
As mentioned above, manifests allow for reproducible profiles, while the
imperative @code{guix install}, @code{guix upgrade}, etc. do not, since they produce
different profiles every time even when they hold the same packages.  See
@uref{https://issues.guix.gnu.org/issue/33285, the related discussion on the matter}.

@item
Manifest specifications are usable by other @samp{guix} commands.  For example, you
can run @code{guix weather -m manifest.scm} to see how many substitutes are
available, which can help you decide whether you want to try upgrading today
or wait a while.  Another example: you can run @code{guix pack -m manifest.scm} to
create a pack containing all the packages in the manifest (and their
transitive references).

@item
Finally, manifests have a Scheme representation, the @samp{<manifest>} record type.
They can be manipulated in Scheme and passed to the various Guix @uref{https://en.wikipedia.org/wiki/Api, APIs}.
@end itemize

It's important to understand that while manifests can be used to declare
profiles, they are not strictly equivalent: profiles have the side effect that
they ``pin'' packages in the store, which prevents them from being
garbage-collected (@pxref{Invoking guix gc,,, guix, GNU Guix Reference Manual})
and ensures that they will still be available at any point in
the future.  The @command{guix shell} command also protects
recently-used profiles from garbage collection; profiles that have not
been used for a while may be garbage-collected though, along with the
packages they refer to.

To be 100% sure that a given profile will never be collected,
install the manifest to a profile and use @code{GUIX_PROFILE=/the/profile;
. "$GUIX_PROFILE"/etc/profile} as explained above: this guarantees that our
hacking environment will be available at all times.

@emph{Security warning:} While keeping old profiles around can be convenient, keep in
mind that outdated packages may not have received the latest security fixes.

@node Reproducible profiles
@subsection Reproducible profiles

To reproduce a profile bit-for-bit, we need two pieces of information:

@itemize
@item
a manifest (@pxref{Writing Manifests,,, guix, GNU Guix Reference Manual});
@item
a Guix channel specification (@pxref{Replicating Guix,,, guix, GNU Guix
Reference Manual}).
@end itemize

Indeed, manifests alone might not be enough: different Guix versions (or
different channels) can produce different outputs for a given manifest.

You can output the Guix channel specification with @samp{guix describe
--format=channels} (@pxref{Invoking guix describe,,, guix, GNU Guix
Reference Manual}).
Save this to a file, say @samp{channel-specs.scm}.

On another computer, you can use the channel specification file and the manifest
to reproduce the exact same profile:

@example
GUIX_EXTRA_PROFILES=$HOME/.guix-extra-profiles
GUIX_EXTRA=$HOME/.guix-extra

mkdir -p "$GUIX_EXTRA"/my-project
guix pull --channels=channel-specs.scm --profile="$GUIX_EXTRA/my-project/guix"

mkdir -p "$GUIX_EXTRA_PROFILES/my-project"
"$GUIX_EXTRA"/my-project/guix/bin/guix package --manifest=/path/to/guix-my-project-manifest.scm --profile="$GUIX_EXTRA_PROFILES"/my-project/my-project
@end example

It's safe to delete the Guix channel profile you've just installed with the
channel specification, the project profile does not depend on it.

@node Software Development
@chapter Software Development

@cindex development, with Guix
@cindex software development, with Guix
Guix is a handy tool for developers; @command{guix shell}, in
particular, gives a standalone development environment for your package,
no matter what language(s) it's written in (@pxref{Invoking guix
shell,,, guix, GNU Guix Reference Manual}).  To benefit from it, you
have to initially write a package definition and have it either in Guix
proper, or in a channel, or directly in your project's source tree as a
@file{guix.scm} file.  This last option is appealing: all developers
have to do to get set up is clone the project's repository and run
@command{guix shell}, with no arguments.

Development needs go beyond development environments though.  How can
developers perform continuous integration of their code in Guix build
environments? How can they deliver their code straight to adventurous
users? This chapter describes a set of files developers can add to their
repository to set up Guix-based development environments, continuous
integration, and continuous delivery---all at once@footnote{This chapter
is adapted from a
@uref{https://guix.gnu.org/en/blog/2023/from-development-environments-to-continuous-integrationthe-ultimate-guide-to-software-development-with-guix/,
blog post} published in June 2023 on the Guix web site.}.

@menu
* Getting Started::             Step 0: using `guix shell'.
* Building with Guix::          Step 1: building your code.
* The Repository as a Channel::  Step 2: turning the repo in a channel.
* Package Variants::            Bonus: Defining variants.
* Setting Up Continuous Integration::  Step 3: continuous integration.
* Build Manifest::              Bonus: Manifest.
* Wrapping Up::                 Recap.
@end menu

@node Getting Started
@section Getting Started

How do we go about ``Guixifying'' a repository? The first step, as we've
seen, will be to add a @file{guix.scm} at the root of the repository in
question. We'll take @uref{https://www.gnu.org/software/guile,Guile} as
an example in this chapter: it's written in Scheme (mostly) and C, and
has a number of dependencies---a C compilation tool chain, C libraries,
Autoconf and its friends, LaTeX, and so on. The resulting
@file{guix.scm} looks like the usual package definition (@pxref{Defining
Packages,,, guix, GNU Guix Reference Manual}), just without the
@code{define-public} bit:

@lisp
;; The ‘guix.scm’ file for Guile, for use by ‘guix shell’.

(use-modules (guix)
             (guix build-system gnu)
             ((guix licenses) #:prefix license:)
             (gnu packages autotools)
             (gnu packages base)
             (gnu packages bash)
             (gnu packages bdw-gc)
             (gnu packages compression)
             (gnu packages flex)
             (gnu packages gdb)
             (gnu packages gettext)
             (gnu packages gperf)
             (gnu packages libffi)
             (gnu packages libunistring)
             (gnu packages linux)
             (gnu packages pkg-config)
             (gnu packages readline)
             (gnu packages tex)
             (gnu packages texinfo)
             (gnu packages version-control))

(package
  (name "guile")
  (version "3.0.99-git")                          ;funky version number
  (source #f)                                     ;no source
  (build-system gnu-build-system)
  (native-inputs
   (append (list autoconf
                 automake
                 libtool
                 gnu-gettext
                 flex
                 texinfo
                 texlive-base                 ;for "make pdf"
                 texlive-epsf
                 gperf
                 git
                 gdb
                 strace
                 readline
                 lzip
                 pkg-config)

           ;; When cross-compiling, a native version of Guile itself is
           ;; needed.
           (if (%current-target-system)
               (list this-package)
               '())))
  (inputs
   (list libffi bash-minimal))
  (propagated-inputs
   (list libunistring libgc))

  (native-search-paths
   (list (search-path-specification
          (variable "GUILE_LOAD_PATH")
          (files '("share/guile/site/3.0")))
         (search-path-specification
          (variable "GUILE_LOAD_COMPILED_PATH")
          (files '("lib/guile/3.0/site-ccache")))))
  (synopsis "Scheme implementation intended especially for extensions")
  (description
   "Guile is the GNU Ubiquitous Intelligent Language for Extensions,
and it's actually a full-blown Scheme implementation!")
  (home-page "https://www.gnu.org/software/guile/")
  (license license:lgpl3+))
@end lisp

Quite a bit of boilerplate, but now someone who'd like to hack on Guile
now only needs to run:

@lisp
guix shell
@end lisp

That gives them a shell containing all the dependencies of Guile: those
listed above, but also @emph{implicit dependencies} such as the GCC tool
chain, GNU@ Make, sed, grep, and so on.  @xref{Invoking guix shell,,,
guix, GNU Guix Reference Manual}, for more info on @command{guix shell}.

@quotation The chef's recommendation
Our suggestion is to create development environments like this:

@example
guix shell --container --link-profile
@end example

@noindent
... or, for short:

@example
guix shell -CP
@end example

That gives a shell in an isolated container, and all the dependencies
show up in @code{$HOME/.guix-profile}, which plays well with caches such
as @file{config.cache} (@pxref{Cache Files,,, autoconf, Autoconf}) and
absolute file names recorded in generated @code{Makefile}s and the
likes. The fact that the shell runs in a container brings peace of mind:
nothing but the current directory and Guile's dependencies is visible
inside the container; nothing from the system can possibly interfere
with your development.
@end quotation

@node Building with Guix
@section Level 1: Building with Guix

Now that we have a package definition (@pxref{Getting Started}), why not
also take advantage of it so we can build Guile with Guix? We had left
the @code{source} field empty, because @command{guix shell} above only
cares about the @emph{inputs} of our package---so it can set up the
development environment---not about the package itself.

To build the package with Guix, we'll need to fill out the @code{source}
field, along these lines:

@lisp
(use-modules (guix)
             (guix git-download)  ;for ‘git-predicate’
             @dots{})

(define vcs-file?
  ;; Return true if the given file is under version control.
  (or (git-predicate (current-source-directory))
      (const #t)))                                ;not in a Git checkout

(package
  (name "guile")
  (version "3.0.99-git")                          ;funky version number
  (source (local-file "." "guile-checkout"
                      #:recursive? #t
                      #:select? vcs-file?))
  @dots{})
@end lisp

Here's what we changed compared to the previous section:

@enumerate 
@item
We added @code{(guix git-download)} to our set of imported modules, so
we can use its @code{git-predicate} procedure.
@item
We defined @code{vcs-file?} as a procedure that returns true when passed
a file that is under version control. For good measure, we add a
fallback case for when we're not in a Git checkout: always return true.
@item
We set @code{source} to a
@uref{https://guix.gnu.org/manual/devel/en/html_node/G_002dExpressions.html#index-local_002dfile,@code{local-file}}---a
recursive copy of the current directory (@code{"."}), limited to files
under version control (the @code{#:select?} bit).
@end enumerate

From there on, our @file{guix.scm} file serves a second purpose: it lets
us build the software with Guix. The whole point of building with Guix
is that it's a ``clean'' build---you can be sure nothing from your
working tree or system interferes with the build result---and it lets
you test a variety of things. First, you can do a plain native build:

@example
guix build -f guix.scm
@end example

But you can also build for another system (possibly after setting up
@pxref{Daemon Offload Setup, offloading,, guix, GNU Guix Reference Manual}
or
@pxref{Virtualization Services, transparent emulation,, guix, GNU Guix
Reference Manual}):

@lisp
guix build -f guix.scm -s aarch64-linux -s riscv64-linux
@end lisp

@noindent
@dots{} or cross-compile:

@lisp
guix build -f guix.scm --target=x86_64-w64-mingw32
@end lisp

You can also use @dfn{package transformations} to test package variants
(@pxref{Package Transformation Options,,, guix, GNU Guix Reference Manual}):

@example
# What if we built with Clang instead of GCC?
guix build -f guix.scm \
  --with-c-toolchain=guile@@3.0.99-git=clang-toolchain

# What about that under-tested configure flag?
guix build -f guix.scm \
  --with-configure-flag=guile@@3.0.99-git=--disable-networking
@end example

Handy!

@node The Repository as a Channel
@section Level 2: The Repository as a Channel

We now have a Git repository containing (among other things) a package
definition (@pxref{Building with Guix}).  Can't we turn it into a
@dfn{channel} (@pxref{Channels,,, guix, GNU Guix Reference Manual})?
After all, channels are designed to ship package definitions to users,
and that's exactly what we're doing with our @file{guix.scm}.

Turns out we can indeed turn it into a channel, but with one caveat: we
must create a separate directory for the @code{.scm} file(s) of our
channel so that @command{guix pull} doesn't load unrelated @code{.scm}
files when someone pulls the channel---and in Guile, there are lots of
them! So we'll start like this, keeping a top-level @file{guix.scm}
symlink for the sake of @command{guix shell}:

@lisp
mkdir -p .guix/modules
mv guix.scm .guix/modules/guile-package.scm
ln -s .guix/modules/guile-package.scm guix.scm
@end lisp

To make it usable as part of a channel, we need to turn our
@file{guix.scm} file into a @dfn{package module} (@pxref{Package
Modules,,, guix, GNU Guix Reference Manual}):
we do that by changing the @code{use-modules} form at the top to a
@code{define-module} form. We also need to actually @emph{export} a
package variable, with @code{define-public}, while still returning the
package value at the end of the file so we can still use
@command{guix shell} and @command{guix build -f guix.scm}. The end result
looks like this (not repeating things that haven't changed):

@lisp
(define-module (guile-package)
  #:use-module (guix)
  #:use-module (guix git-download)   ;for ‘git-predicate’
  @dots{})

(define vcs-file?
  ;; Return true if the given file is under version control.
  (or (git-predicate (dirname (dirname (current-source-directory))))
      (const #t)))                                ;not in a Git checkout

(define-public guile
  (package
    (name "guile")
    (version "3.0.99-git")                          ;funky version number
    (source (local-file "../.." "guile-checkout"
                        #:recursive? #t
                        #:select? vcs-file?))
    @dots{}))

;; Return the package object define above at the end of the module.
guile
@end lisp

We need one last thing: a
@uref{https://guix.gnu.org/manual/devel/en/html_node/Package-Modules-in-a-Sub_002ddirectory.html,@code{.guix-channel}
file} so Guix knows where to look for package modules in our repository:

@lisp
;; This file lets us present this repo as a Guix channel.

(channel
  (version 0)
  (directory ".guix/modules"))  ;look for package modules under .guix/modules/
@end lisp

To recap, we now have these files:

@lisp
.
├── .guix-channel
├── guix.scm → .guix/modules/guile-package.scm
└── .guix
    └── modules
       └── guile-package.scm
@end lisp

And that's it: we have a channel! (We could do better and support
@uref{https://guix.gnu.org/manual/devel/en/html_node/Specifying-Channel-Authorizations.html,@emph{channel
authentication}} so users know they're pulling genuine code. We'll spare
you the details here but it's worth considering!) Users can pull from
this channel by
@uref{https://guix.gnu.org/manual/devel/en/html_node/Specifying-Additional-Channels.html,adding
it to @code{~/.config/guix/channels.scm}}, along these lines:

@lisp
(append (list (channel
                (name 'guile)
                (url "https://git.savannah.gnu.org/git/guile.git")
                (branch "main")))
        %default-channels)
@end lisp

After running @command{guix pull}, we can see the new package:

@example
$ guix describe
Generation 264  May 26 2023 16:00:35    (current)
  guile 36fd2b4
    repository URL: https://git.savannah.gnu.org/git/guile.git
    branch: main
    commit: 36fd2b4920ae926c79b936c29e739e71a6dff2bc
  guix c5bc698
    repository URL: https://git.savannah.gnu.org/git/guix.git
    commit: c5bc698e8922d78ed85989985cc2ceb034de2f23
$ guix package -A ^guile$
guile   3.0.99-git      out,debug       guile-package.scm:51:4
guile   3.0.9           out,debug       gnu/packages/guile.scm:317:2
guile   2.2.7           out,debug       gnu/packages/guile.scm:258:2
guile   2.2.4           out,debug       gnu/packages/guile.scm:304:2
guile   2.0.14          out,debug       gnu/packages/guile.scm:148:2
guile   1.8.8           out             gnu/packages/guile.scm:77:2
$ guix build guile@@3.0.99-git
[@dots{}]
/gnu/store/axnzbl89yz7ld78bmx72vpqp802dwsar-guile-3.0.99-git-debug
/gnu/store/r34gsij7f0glg2fbakcmmk0zn4v62s5w-guile-3.0.99-git
@end example

That's how, as a developer, you get your software delivered directly
into the hands of users! No intermediaries, yet no loss of transparency
and provenance tracking.

With that in place, it also becomes trivial for anyone to create Docker
images, Deb/RPM packages, or a plain tarball with @command{guix pack}
(@pxref{Invoking guix pack,,, guix, GNU Guix Reference Manual}):

@example
# How about a Docker image of our Guile snapshot?
guix pack -f docker -S /bin=bin guile@@3.0.99-git

# And a relocatable RPM?
guix pack -f rpm -R -S /bin=bin guile@@3.0.99-git
@end example

@node Package Variants
@section Bonus: Package Variants

We now have an actual channel, but it contains only one package
(@pxref{The Repository as a Channel}).  While we're at it, we can define
@dfn{package variants} (@pxref{Defining Package Variants,,, guix, GNU
Guix Reference Manual}) in our @file{guile-package.scm} file, variants
that we want to be able to test as Guile developers---similar to what we
did above with transformation options. We can add them like so:

@lisp
;; This is the ‘.guix/modules/guile-package.scm’ file.

(define-module (guile-package)
  @dots{})

(define-public guile
  @dots{})

(define (package-with-configure-flags p flags)
  "Return P with FLAGS as additional 'configure' flags."
  (package/inherit p
    (arguments
     (substitute-keyword-arguments (package-arguments p)
       ((#:configure-flags original-flags #~(list))
        #~(append #$original-flags #$flags))))))

(define-public guile-without-threads
  (package
    (inherit (package-with-configure-flags guile
                                           #~(list "--without-threads")))
    (name "guile-without-threads")))

(define-public guile-without-networking
  (package
    (inherit (package-with-configure-flags guile
                                           #~(list "--disable-networking")))
    (name "guile-without-networking")))


;; Return the package object defined above at the end of the module.
guile
@end lisp

We can build these variants as regular packages once we've pulled the
channel. Alternatively, from a checkout of Guile, we can run a command
like this one from the top level:

@lisp
guix build -L $PWD/.guix/modules guile-without-threads
@end lisp

@node Setting Up Continuous Integration
@section Level 3: Setting Up Continuous Integration

@cindex continuous integration (CI)
The channel we defined above (@pxref{The Repository as a Channel})
becomes even more interesting once we set up
@uref{https://en.wikipedia.org/wiki/Continuous_integration,
@dfn{continuous integration}} (CI). There are several ways to do that.

You can use one of the mainstream continuous integration tools, such as
GitLab-CI. To do that, you need to make sure you run jobs in a Docker
image or virtual machine that has Guix installed. If we were to do that
in the case of Guile, we'd have a job that runs a shell command like
this one:

@lisp
guix build -L $PWD/.guix/modules guile@@3.0.99-git
@end lisp

Doing this works great and has the advantage of being easy to achieve on
your favorite CI platform.

That said, you'll really get the most of it by using
@uref{https://guix.gnu.org/en/cuirass,Cuirass}, a CI tool designed for
and tightly integrated with Guix. Using it is more work than using a
hosted CI tool because you first need to set it up, but that setup phase
is greatly simplified if you use its Guix System service
(@pxref{Continuous Integration,,, guix, GNU Guix Reference Manual}).
Going back to our example, we give Cuirass a spec file that goes like
this:

@lisp
;; Cuirass spec file to build all the packages of the ‘guile’ channel.
(list (specification
        (name "guile")
        (build '(channels guile))
        (channels
         (append (list (channel
                         (name 'guile)
                         (url "https://git.savannah.gnu.org/git/guile.git")
                         (branch "main")))
                 %default-channels))))
@end lisp

It differs from what you'd do with other CI tools in two important ways:

@itemize
@item
Cuirass knows it's tracking @emph{two} channels, @code{guile} and
@code{guix}. Indeed, our own @code{guile} package depends on many
packages provided by the @code{guix} channel---GCC, the GNU libc,
libffi, and so on. Changes to packages from the @code{guix} channel can
potentially influence our @code{guile} build and this is something we'd
like to see as soon as possible as Guile developers.
@item
Build results are not thrown away: they can be distributed as
@dfn{substitutes} so that users of our @code{guile} channel
transparently get pre-built binaries!  (@pxref{Substitutes,,, guix, GNU
Guix Reference Manual}, for background info on substitutes.)
@end itemize

From a developer's viewpoint, the end result is this
@uref{https://ci.guix.gnu.org/jobset/guile,status page} listing
@emph{evaluations}: each evaluation is a combination of commits of the
@code{guix} and @code{guile} channels providing a number of
@emph{jobs}---one job per package defined in @file{guile-package.scm}
times the number of target architectures.

As for substitutes, they come for free! As an example, since our
@code{guile} jobset is built on ci.guix.gnu.org, which runs
@command{guix publish} (@pxref{Invoking guix publish,,, guix, GNU Guix
Reference Manual}) in addition to Cuirass, one automatically gets
substitutes for @code{guile} builds from ci.guix.gnu.org; no additional
work is needed for that.

@node Build Manifest
@section Bonus: Build manifest

The Cuirass spec above is convenient: it builds every package in our
channel, which includes a few variants (@pxref{Setting Up Continuous
Integration}).  However, this might be insufficiently expressive in some
cases: one might want specific cross-compilation jobs, transformations,
Docker images, RPM/Deb packages, or even system tests.

To achieve that, you can write a @dfn{manifest} (@pxref{Writing
Manifests,,, guix, GNU Guix Reference Manual}).  The one we have for
Guile has entries for the package variants we defined above, as well as
additional variants and cross builds:

@lisp
;; This is ‘.guix/manifest.scm’.

(use-modules (guix)
             (guix profiles)
             (guile-package))   ;import our own package module

(define* (package->manifest-entry* package system
                                   #:key target)
  "Return a manifest entry for PACKAGE on SYSTEM, optionally cross-compiled to
TARGET."
  (manifest-entry
    (inherit (package->manifest-entry package))
    (name (string-append (package-name package) "." system
                         (if target
                             (string-append "." target)
                             "")))
    (item (with-parameters ((%current-system system)
                            (%current-target-system target))
            package))))

(define native-builds
  (manifest
   (append (map (lambda (system)
                  (package->manifest-entry* guile system))

                '("x86_64-linux" "i686-linux"
                  "aarch64-linux" "armhf-linux"
                  "powerpc64le-linux"))
           (map (lambda (guile)
                  (package->manifest-entry* guile "x86_64-linux"))
                (cons (package
                        (inherit (package-with-c-toolchain
                                  guile
                                  `(("clang-toolchain"
                                     ,(specification->package
                                       "clang-toolchain")))))
                        (name "guile-clang"))
                      (list guile-without-threads
                            guile-without-networking
                            guile-debug
                            guile-strict-typing))))))

(define cross-builds
  (manifest
   (map (lambda (target)
          (package->manifest-entry* guile "x86_64-linux"
                                    #:target target))
        '("i586-pc-gnu"
          "aarch64-linux-gnu"
          "riscv64-linux-gnu"
          "i686-w64-mingw32"
          "x86_64-linux-gnu"))))

(concatenate-manifests (list native-builds cross-builds))
@end lisp

We won't go into the details of this manifest; suffice to say that it
provides additional flexibility. We now need to tell Cuirass to build
this manifest, which is done with a spec slightly different from the
previous one:

@lisp
;; Cuirass spec file to build all the packages of the ‘guile’ channel.
(list (specification
        (name "guile")
        (build '(manifest ".guix/manifest.scm"))
        (channels
         (append (list (channel
                         (name 'guile)
                         (url "https://git.savannah.gnu.org/git/guile.git")
                         (branch "main")))
                 %default-channels))))
@end lisp

We changed the @code{(build @dots{})} part of the spec to
@code{'(manifest ".guix/manifest.scm")} so that it would pick our
manifest, and that's it!

@node Wrapping Up
@section Wrapping Up

We picked Guile as the running example in this chapter and you can see
the result here:

@itemize
@item
@uref{https://git.savannah.gnu.org/cgit/guile.git/tree/.guix-channel?id=cd57379b3df636198d8cd8e76c1bfbc523762e79,@code{.guix-channel}};
@item
@uref{https://git.savannah.gnu.org/cgit/guile.git/tree/.guix/modules/guile-package.scm?id=cd57379b3df636198d8cd8e76c1bfbc523762e79,@code{.guix/modules/guile-package.scm}}
with the top-level @file{guix.scm} symlink;
@item
@uref{https://git.savannah.gnu.org/cgit/guile.git/tree/.guix/manifest.scm?id=cd57379b3df636198d8cd8e76c1bfbc523762e79,@code{.guix/manifest.scm}}.
@end itemize

These days, repositories are commonly peppered with dot files for
various tools: @code{.envrc}, @code{.gitlab-ci.yml},
@code{.github/workflows}, @code{Dockerfile}, @code{.buildpacks},
@code{Aptfile}, @code{requirements.txt}, and whatnot. It may sound like
we're proposing a bunch of @emph{additional} files, but in fact those
files are expressive enough to @emph{supersede} most or all of those
listed above.

With a couple of files, we get support for:

@itemize
@item
development environments (@command{guix shell});
@item
pristine test builds, including for package variants and for
cross-compilation (@command{guix build});
@item
continuous integration (with Cuirass or with some other tool);
@item
continuous delivery to users (@emph{via} the channel and with pre-built
binaries);
@item
generation of derivative build artifacts such as Docker images or
Deb/RPM packages (@command{guix pack}).
@end itemize

This a nice (in our view!) unified tool set for reproducible software
deployment, and an illustration of how you as a developer can benefit
from it!


@c *********************************************************************
@node Environment management
@chapter Environment management

Guix provides multiple tools to manage environment.  This chapter
demonstrate such utilities.

@menu
* Guix environment via direnv::  Setup Guix environment with direnv
@end menu

@node Guix environment via direnv
@section Guix environment via direnv

Guix provides a @samp{direnv} package, which could extend shell after
directory change.  This tool could be used to prepare a pure Guix
environment.

The following example provides a shell function for @file{~/.direnvrc}
file, which could be used from Guix Git repository in
@file{~/src/guix/.envrc} file to setup a build environment similar to
described in @pxref{Building from Git,,, guix, GNU Guix Reference
Manual}.

Create a @file{~/.direnvrc} with a Bash code:

@example
# Thanks <https://github.com/direnv/direnv/issues/73#issuecomment-152284914>
export_function()
@{
  local name=$1
  local alias_dir=$PWD/.direnv/aliases
  mkdir -p "$alias_dir"
  PATH_add "$alias_dir"
  local target="$alias_dir/$name"
  if declare -f "$name" >/dev/null; then
    echo "#!$SHELL" > "$target"
    declare -f "$name" >> "$target" 2>/dev/null
    # Notice that we add shell variables to the function trigger.
    echo "$name \$*" >> "$target"
    chmod +x "$target"
  fi
@}

use_guix()
@{
    # Set GitHub token.
    export GUIX_GITHUB_TOKEN="xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"

    # Unset 'GUIX_PACKAGE_PATH'.
    export GUIX_PACKAGE_PATH=""

    # Recreate a garbage collector root.
    gcroots="$HOME/.config/guix/gcroots"
    mkdir -p "$gcroots"
    gcroot="$gcroots/guix"
    if [ -L "$gcroot" ]
    then
        rm -v "$gcroot"
    fi

    # Miscellaneous packages.
    PACKAGES_MAINTENANCE=(
        direnv
        git
        git:send-email
        git-cal
        gnupg
        guile-colorized
        guile-readline
        less
        ncurses
        openssh
        xdot
    )

    # Environment packages.
    PACKAGES=(help2man guile-sqlite3 guile-gcrypt)

    # Thanks <https://lists.gnu.org/archive/html/guix-devel/2016-09/msg00859.html>
    eval "$(guix environment --search-paths --root="$gcroot" --pure guix --ad-hoc $@{PACKAGES[@@]@} $@{PACKAGES_MAINTENANCE[@@]@} "$@@")"

    # Predefine configure flags.
    configure()
    @{
        ./configure --localstatedir=/var --prefix=
    @}
    export_function configure

    # Run make and optionally build something.
    build()
    @{
        make -j 2
        if [ $# -gt 0 ]
        then
            ./pre-inst-env guix build "$@@"
        fi
    @}
    export_function build

    # Predefine push Git command.
    push()
    @{
        git push --set-upstream origin
    @}
    export_function push

    clear                        # Clean up the screen.
    git-cal --author='Your Name' # Show contributions calendar.

    # Show commands help.
    echo "
build          build a package or just a project if no argument provided
configure      run ./configure with predefined parameters
push           push to upstream Git repository
"
@}
@end example

Every project containing @file{.envrc} with a string @code{use guix}
will have predefined environment variables and procedures.

Run @command{direnv allow} to setup the environment for the first time.


@c *********************************************************************
@node Installing Guix on a Cluster
@chapter Installing Guix on a Cluster

@cindex cluster installation
@cindex high-performance computing, HPC
@cindex HPC, high-performance computing
Guix is appealing to scientists and @acronym{HPC, high-performance
computing} practitioners: it makes it easy to deploy potentially complex
software stacks, and it lets you do so in a reproducible fashion---you
can redeploy the exact same software on different machines and at
different points in time.

In this chapter we look at how a cluster sysadmin can install Guix for
system-wide use, such that it can be used on all the cluster nodes, and
discuss the various tradeoffs@footnote{This chapter is adapted from a
@uref{https://hpc.guix.info/blog/2017/11/installing-guix-on-a-cluster/,
blog post published on the Guix-HPC web site in 2017}.}.

@quotation Note
Here we assume that the cluster is running a GNU/Linux distro other than
Guix System and that we are going to install Guix on top of it.
@end quotation

@menu
* Setting Up a Head Node::      The node that runs the daemon.
* Setting Up Compute Nodes::    Client nodes.
* Cluster Network Access::      Dealing with network access restrictions.
* Cluster Disk Usage::          Disk usage considerations.
* Cluster Security Considerations::  Keeping the cluster secure.
@end menu

@node Setting Up a Head Node
@section Setting Up a Head Node

The recommended approach is to set up one @emph{head node} running
@command{guix-daemon} and exporting @file{/gnu/store} over NFS to
compute nodes.

Remember that @command{guix-daemon} is responsible for spawning build
processes and downloads on behalf of clients (@pxref{Invoking
guix-daemon,,, guix, GNU Guix Reference Manual}), and more generally
accessing @file{/gnu/store}, which contains all the package binaries
built by all the users (@pxref{The Store,,, guix, GNU Guix Reference
Manual}).  ``Client'' here refers to all the Guix commands that users
see, such as @code{guix install}.  On a cluster, these commands may be
running on the compute nodes and we'll want them to talk to the head
node's @code{guix-daemon} instance.

To begin with, the head node can be installed following the usual binary
installation instructions (@pxref{Binary Installation,,, guix, GNU Guix
Reference Manual}).  Thanks to the installation script, this should be
quick.  Once installation is complete, we need to make some adjustments.

Since we want @code{guix-daemon} to be reachable not just from the head
node but also from the compute nodes, we need to arrange so that it
listens for connections over TCP/IP.  To do that, we'll edit the systemd
startup file for @command{guix-daemon},
@file{/etc/systemd/system/guix-daemon.service}, and add a
@code{--listen} argument to the @code{ExecStart} line so that it looks
something like this:

@example
ExecStart=/var/guix/profiles/per-user/root/current-guix/bin/guix-daemon --build-users-group=guixbuild --listen=/var/guix/daemon-socket/socket --listen=0.0.0.0
@end example

For these changes to take effect, the service needs to be restarted:

@example
systemctl daemon-reload
systemctl restart guix-daemon
@end example

@quotation Note
The @code{--listen=0.0.0.0} bit means that @code{guix-daemon} will
process @emph{all} incoming TCP connections on port 44146
(@pxref{Invoking guix-daemon,,, guix, GNU Guix Reference Manual}). This
is usually fine in a cluster setup where the head node is reachable
exclusively from the cluster's local area network---you don't want that
to be exposed to the Internet!
@end quotation

The next step is to define our NFS exports in
@uref{https://linux.die.net/man/5/exports,@file{/etc/exports}} by adding
something along these lines:

@example
/gnu/store    *(ro)
/var/guix     *(rw, async)
/var/log/guix *(ro)
@end example

The @file{/gnu/store} directory can be exported read-only since only
@command{guix-daemon} on the master node will ever modify it.
@file{/var/guix} contains @emph{user profiles} as managed by @code{guix
package}; thus, to allow users to install packages with @code{guix
package}, this must be read-write.

Users can create as many profiles as they like in addition to the
default profile, @file{~/.guix-profile}.  For instance, @code{guix
package -p ~/dev/python-dev -i python} installs Python in a profile
reachable from the @code{~/dev/python-dev} symlink.  To make sure that
this profile is protected from garbage collection---i.e., that Python
will not be removed from @file{/gnu/store} while this profile exists---,
@emph{home directories should be mounted on the head node} as well so
that @code{guix-daemon} knows about these non-standard profiles and
avoids collecting software they refer to.

It may be a good idea to periodically remove unused bits from
@file{/gnu/store} by running @command{guix gc} (@pxref{Invoking guix
gc,,, guix, GNU Guix Reference Manual}).  This can be done by adding a
crontab entry on the head node:

@example
root@@master# crontab -e
@end example

@noindent
... with something like this:

@example
# Every day at 5AM, run the garbage collector to make sure
# at least 10 GB are free on /gnu/store.
0 5 * * 1  /usr/local/bin/guix gc -F10G
@end example

We're done with the head node! Let's look at compute nodes now.

@node Setting Up Compute Nodes
@section Setting Up Compute Nodes

First of all, we need compute nodes to mount those NFS directories that
the head node exports.  This can be done by adding the following lines
to @uref{https://linux.die.net/man/5/fstab,@file{/etc/fstab}}:

@example
@var{head-node}:/gnu/store    /gnu/store    nfs  defaults,_netdev,vers=3 0 0
@var{head-node}:/var/guix     /var/guix     nfs  defaults,_netdev,vers=3 0 0
@var{head-node}:/var/log/guix /var/log/guix nfs  defaults,_netdev,vers=3 0 0
@end example

@noindent
... where @var{head-node} is the name or IP address of your head node.
From there on, assuming the mount points exist, you should be able to
mount each of these on the compute nodes.

Next, we need to provide a default @command{guix} command that users can
run when they first connect to the cluster (eventually they will invoke
@command{guix pull}, which will provide them with their ``own''
@command{guix} command).  Similar to what the binary installation script
did on the head node, we'll store that in @file{/usr/local/bin}:

@example
mkdir -p /usr/local/bin
ln -s /var/guix/profiles/per-user/root/current-guix/bin/guix \
      /usr/local/bin/guix
@end example

We then need to tell @code{guix} to talk to the daemon running on our
master node, by adding these lines to @code{/etc/profile}:

@example
GUIX_DAEMON_SOCKET="guix://@var{head-node}"
export GUIX_DAEMON_SOCKET
@end example

To avoid warnings and make sure @code{guix} uses the right locale, we
need to tell it to use locale data provided by Guix (@pxref{Application
Setup,,, guix, GNU Guix Reference Manual}):

@example
GUIX_LOCPATH=/var/guix/profiles/per-user/root/guix-profile/lib/locale
export GUIX_LOCPATH

# Here we must use a valid locale name.  Try "ls $GUIX_LOCPATH/*"
# to see what names can be used.
LC_ALL=fr_FR.utf8
export LC_ALL
@end example

For convenience, @code{guix package} automatically generates
@file{~/.guix-profile/etc/profile}, which defines all the environment
variables necessary to use the packages---@code{PATH},
@code{C_INCLUDE_PATH}, @code{PYTHONPATH}, etc.  Thus it's a good idea to
source it from @code{/etc/profile}:

@example
GUIX_PROFILE="$HOME/.guix-profile"
if [ -f "$GUIX_PROFILE/etc/profile" ]; then
  . "$GUIX_PROFILE/etc/profile"
fi
@end example

Last but not least, Guix provides command-line completion notably for
Bash and zsh.  In @code{/etc/bashrc}, consider adding this line:

@verbatim
. /var/guix/profiles/per-user/root/current-guix/etc/bash_completion.d/guix
@end verbatim

Voilà!

You can check that everything's in place by logging in on a compute node
and running:

@example
guix install hello
@end example

The daemon on the head node should download pre-built binaries on your
behalf and unpack them in @file{/gnu/store}, and @command{guix install}
should create @file{~/.guix-profile} containing the
@file{~/.guix-profile/bin/hello} command.

@node Cluster Network Access
@section Network Access

Guix requires network access to download source code and pre-built
binaries.  The good news is that only the head node needs that since
compute nodes simply delegate to it.

It is customary for cluster nodes to have access at best to a
@emph{white list} of hosts.  Our head node needs at least
@code{ci.guix.gnu.org} in this white list since this is where it gets
pre-built binaries from by default, for all the packages that are in
Guix proper.

Incidentally, @code{ci.guix.gnu.org} also serves as a
@emph{content-addressed mirror} of the source code of those packages.
Consequently, it is sufficient to have @emph{only}
@code{ci.guix.gnu.org} in that white list.

Software packages maintained in a separate repository such as one of the
various @uref{https://hpc.guix.info/channels, HPC channels} are of
course unavailable from @code{ci.guix.gnu.org}.  For these packages, you
may want to extend the white list such that source and pre-built
binaries (assuming this-party servers provide binaries for these
packages) can be downloaded.  As a last resort, users can always
download source on their workstation and add it to the cluster's
@file{/gnu/store}, like this:

@verbatim
GUIX_DAEMON_SOCKET=ssh://compute-node.example.org \
  guix download http://starpu.gforge.inria.fr/files/starpu-1.2.3/starpu-1.2.3.tar.gz
@end verbatim

The above command downloads @code{starpu-1.2.3.tar.gz} @emph{and} sends
it to the cluster's @code{guix-daemon} instance over SSH.

Air-gapped clusters require more work.  At the moment, our suggestion
would be to download all the necessary source code on a workstation
running Guix.  For instance, using the @option{--sources} option of
@command{guix build} (@pxref{Invoking guix build,,, guix, GNU Guix
Reference Manual}), the example below downloads all the source code the
@code{openmpi} package depends on:

@example
$ guix build --sources=transitive openmpi

@dots{}

/gnu/store/xc17sm60fb8nxadc4qy0c7rqph499z8s-openmpi-1.10.7.tar.bz2
/gnu/store/s67jx92lpipy2nfj5cz818xv430n4b7w-gcc-5.4.0.tar.xz
/gnu/store/npw9qh8a46lrxiwh9xwk0wpi3jlzmjnh-gmp-6.0.0a.tar.xz
/gnu/store/hcz0f4wkdbsvsdky3c0vdvcawhdkyldb-mpfr-3.1.5.tar.xz
/gnu/store/y9akh452n3p4w2v631nj0injx7y0d68x-mpc-1.0.3.tar.gz
/gnu/store/6g5c35q8avfnzs3v14dzl54cmrvddjm2-glibc-2.25.tar.xz
/gnu/store/p9k48dk3dvvk7gads7fk30xc2pxsd66z-hwloc-1.11.8.tar.bz2
/gnu/store/cry9lqidwfrfmgl0x389cs3syr15p13q-gcc-5.4.0.tar.xz
/gnu/store/7ak0v3rzpqm2c5q1mp3v7cj0rxz0qakf-libfabric-1.4.1.tar.bz2
/gnu/store/vh8syjrsilnbfcf582qhmvpg1v3rampf-rdma-core-14.tar.gz
…
@end example

(In case you're wondering, that's more than 320@ MiB of
@emph{compressed} source code.)

We can then make a big archive containing all of this (@pxref{Invoking
guix archive,,, guix, GNU Guix Reference Manual}):

@verbatim
$ guix archive --export \
    `guix build --sources=transitive openmpi` \
    > openmpi-source-code.nar
@end verbatim

@dots{} and we can eventually transfer that archive to the cluster on
removable storage and unpack it there:

@verbatim
$ guix archive --import < openmpi-source-code.nar
@end verbatim

This process has to be repeated every time new source code needs to be
brought to the cluster.

As we write this, the research institutes involved in Guix-HPC do not
have air-gapped clusters though. If you have experience with such
setups, we would like to hear feedback and suggestions.

@node Cluster Disk Usage
@section Disk Usage

@cindex disk usage, on a cluster
A common concern of sysadmins' is whether this is all going to eat a lot
of disk space.  If anything, if something is going to exhaust disk
space, it's going to be scientific data sets rather than compiled
software---that's our experience with almost ten years of Guix usage on
HPC clusters.  Nevertheless, it's worth taking a look at how Guix
contributes to disk usage.

First, having several versions or variants of a given package in
@file{/gnu/store} does not necessarily cost much, because
@command{guix-daemon} implements deduplication of identical files, and
package variants are likely to have a number of common files.

As mentioned above, we recommend having a cron job to run @code{guix gc}
periodically, which removes @emph{unused} software from
@file{/gnu/store}. However, there's always a possibility that users will
keep lots of software in their profiles, or lots of old generations of
their profiles, which is ``live'' and cannot be deleted from the
viewpoint of @command{guix gc}.

The solution to this is for users to regularly remove old generations of
their profile. For instance, the following command removes generations
that are more than two-month old:

@example
guix package --delete-generations=2m
@end example

Likewise, it's a good idea to invite users to regularly upgrade their
profile, which can reduce the number of variants of a given piece of
software stored in @file{/gnu/store}:

@example
guix pull
guix upgrade
@end example

As a last resort, it is always possible for sysadmins to do some of this
on behalf of their users. Nevertheless, one of the strengths of Guix is
the freedom and control users get on their software environment, so we
strongly recommend leaving users in control.

@node Cluster Security Considerations
@section Security Considerations

@cindex security, on a cluster
On an HPC cluster, Guix is typically used to manage scientific software.
Security-critical software such as the operating system kernel and
system services such as @code{sshd} and the batch scheduler remain under
control of sysadmins.

The Guix project has a good track record delivering security updates in
a timely fashion (@pxref{Security Updates,,, guix, GNU Guix Reference
Manual}).  To get security updates, users have to run @code{guix pull &&
guix upgrade}.

Because Guix uniquely identifies software variants, it is easy to see if
a vulnerable piece of software is in use. For instance, to check whether
the glibc@ 2.25 variant without the mitigation patch against
``@uref{https://www.qualys.com/2017/06/19/stack-clash/stack-clash.txt,Stack
Clash}'', one can check whether user profiles refer to it at all:

@example
guix gc --referrers /gnu/store/…-glibc-2.25
@end example

This will report whether profiles exist that refer to this specific
glibc variant.


@c *********************************************************************
@node Acknowledgments
@chapter Acknowledgments

Guix is based on the @uref{https://nixos.org/nix/, Nix package manager},
which was designed and
implemented by Eelco Dolstra, with contributions from other people (see
the @file{nix/AUTHORS} file in Guix.)  Nix pioneered functional package
management, and promoted unprecedented features, such as transactional
package upgrades and rollbacks, per-user profiles, and referentially
transparent build processes.  Without this work, Guix would not exist.

The Nix-based software distributions, Nixpkgs and NixOS, have also been
an inspiration for Guix.

GNU@tie{}Guix itself is a collective work with contributions from a
number of people.  See the @file{AUTHORS} file in Guix for more
information on these fine people.  The @file{THANKS} file lists people
who have helped by reporting bugs, taking care of the infrastructure,
providing artwork and themes, making suggestions, and more---thank you!

This document includes adapted sections from articles that have
previously been published on the Guix blog at
@uref{https://guix.gnu.org/blog} and on the Guix-HPC blog at
@uref{https://hpc.guix.info/blog}.


@c *********************************************************************
@node GNU Free Documentation License
@appendix GNU Free Documentation License
@cindex license, GNU Free Documentation License
@include fdl-1.3.texi

@c *********************************************************************
@node Concept Index
@unnumbered Concept Index
@printindex cp

@bye

@c Local Variables:
@c ispell-local-dictionary: "american";
@c End: