system: Add "guix system docker-image" command.

* gnu/system/vm.scm (system-docker-image): New procedure.
* guix/scripts/system.scm (system-derivation-for-action): Add a case for
  docker-image, and in that case, call system-docker-image.
  (show-help): Document docker-image.
  (guix-system): Parse arguments for docker-image.
* doc/guix.texi (Invoking guix system): Document "guix system
  docker-image".
* gnu/system/examples/docker-image.tmpl: New file.

1 files changed, 47 insertions, 0 deletions

diff --git a/gnu/system/examples/docker-image.tmpl b/gnu/system/examples/docker-image.tmpl
new file mode 100644
index 0000000000..d73187398f
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+++ b/gnu/system/examples/docker-image.tmpl
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+;; This is an operating system configuration template for a "Docker image"
+;; setup, so it has barely any services at all.
+
+(use-modules (gnu))
+
+(operating-system
+  (host-name "komputilo")
+  (timezone "Europe/Berlin")
+  (locale "en_US.utf8")
+
+  ;; This is where user accounts are specified.  The "root" account is
+  ;; implicit, and is initially created with the empty password.
+  (users (cons (user-account
+                (name "alice")
+                (comment "Bob's sister")
+                (group "users")
+                (supplementary-groups '("wheel"
+                                        "audio" "video"))
+                (home-directory "/home/alice"))
+               %base-user-accounts))
+
+  ;; Globally-installed packages.
+  (packages %base-packages)
+
+  ;; Because the system will run in a Docker container, we may omit many
+  ;; things that would normally be required in an operating system
+  ;; configuration file.  These things include:
+  ;;
+  ;;   * bootloader
+  ;;   * file-systems
+  ;;   * services such as mingetty, udevd, slim, networking, dhcp
+  ;;
+  ;; Either these things are simply not required, or Docker provides
+  ;; similar services for us.
+
+  ;; This will be ignored.
+  (bootloader (bootloader-configuration
+               (bootloader grub-bootloader)
+               (target "does-not-matter")))
+  ;; This will be ignored, too.
+  (file-systems (list (file-system
+                        (device "does-not-matter")
+                        (mount-point "/")
+                        (type "does-not-matter"))))
+
+  ;; Guix is all you need!
+  (services (list (guix-service))))