guix system: Add 'delete-generations'.

* guix/scripts/package.scm (delete-matching-generations): Export.
* guix/scripts/system.scm (show-help): Add 'delete-generations'.
(process-command): Honor it.
(guix-system): Support it.
* doc/guix.texi (Invoking guix system): Document it.

1 files changed, 26 insertions, 0 deletions

diff --git a/doc/guix.texi b/doc/guix.texi
index 2ae4f53245..6980672094 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -23038,6 +23038,32 @@ Currently, as with @command{switch-generation}, you must reboot after
 running this action to actually start using the preceding system
 generation.
 
+@item delete-generations
+@cindex deleting system generations
+@cindex saving space
+Delete system generations, making them candidates for garbage collection
+(@pxref{Invoking guix gc}, for information on how to run the ``garbage
+collector'').
+
+This works in the same way as @command{guix package --delete-generations}
+(@pxref{Invoking guix package, @code{--delete-generations}}).  With no
+arguments, all system generations but the current one are deleted:
+
+@example
+guix system delete-generations
+@end example
+
+You can also select the generations you want to delete.  The example below
+deletes all the system generations that are more than two month old:
+
+@example
+guix system delete-generations 2m
+@end example
+
+Running this command automatically reinstalls the bootloader with an updated
+list of menu entries---e.g., the ``old generations'' sub-menu in GRUB no
+longer lists the generations that have been deleted.
+
 @item build
 Build the derivation of the operating system, which includes all the
 configuration files and programs needed to boot and run the system.