pack: Add '--entry-point'.

* guix/scripts/pack.scm (self-contained-tarball): Add #:entry-point and
warn when it's true.
(squashfs-image): Add #:entry-point and honor it.
(docker-image): Add #:entry-point and honor it.
(%options, show-help): Add '--entry-point'.
(guix-pack): Honor '--entry-point' and pass #:entry-point to BUILD-IMAGE.
* gnu/tests/docker.scm (run-docker-test): Test 'docker run' with the
default entry point.
(build-tarball&run-docker-test): Pass #:entry-point to 'docker-image'.
* doc/guix.texi (Invoking guix pack): Document it.
* gnu/tests/singularity.scm (run-singularity-test)["singularity run"]:
New test.
(build-tarball&run-singularity-test): Pass #:entry-point to
'squashfs-image'.

1 files changed, 23 insertions, 0 deletions

diff --git a/doc/guix.texi b/doc/guix.texi
index d37d63066f..bd0f3e8fd5 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -4866,6 +4866,29 @@ advantage to work without requiring special kernel support, but it incurs
 run-time overhead every time a system call is made.
 @end quotation
 
+@cindex entry point, for Docker images
+@item --entry-point=@var{command}
+Use @var{command} as the @dfn{entry point} of the resulting pack, if the pack
+format supports it---currently @code{docker} and @code{squashfs} (Singularity)
+support it.  @var{command} must be relative to the profile contained in the
+pack.
+
+The entry point specifies the command that tools like @code{docker run} or
+@code{singularity run} automatically start by default.  For example, you can
+do:
+
+@example
+guix pack -f docker --entry-point=bin/guile guile
+@end example
+
+The resulting pack can easily be loaded and @code{docker run} with no extra
+arguments will spawn @code{bin/guile}:
+
+@example
+docker load -i pack.tar.gz
+docker run @var{image-id}
+@end example
+
 @item --expression=@var{expr}
 @itemx -e @var{expr}
 Consider the package @var{expr} evaluates to.