bug#34913: ‘guix pack -f squashfs’ absolute symlinks confuse Singularity 2.x

[Ludovic Courtès]

Hello,

‘guix pack -f squashfs -S /bin=bin bash …’ produces a file system that
contains symlinks with absolute targets.

Unfortunately, Singularity 2.x erroneously checks for symlink validity
before chroot’ing into the file system.  Thus all these absolute
symlinks appear to be dangling (unless the host happens to have those
symlink targets…).

I reported this a while back but this hasn’t been fixed in 2.x (the new
3.x code base doesn’t seem to have this problem):

  https://github.com/sylabs/singularity/issues/1487

The effect of this bug is that our images appear to be unusable with
Singularity 2.x, at least if you don’t manually adjust the file system
to fix those symlinks:

--8<---------------cut here---------------start------------->8---
$ singularity exec bash.sqsh /bin/sh
ERROR  : No valid /bin/sh in container
ABORT  : Retval = 255
--8<---------------cut here---------------end--------------->8---

Ludo’.