guix pack -f squashfs ...

[Yoshinori Arai]

I'm trying guix pack -f squashfs ...
$ guix pack -f squashfs guile emacs geiser
$ cp /gnu/store/jy7k2g48303jlz5hlaflrsa4mdrbhcy6-squashfs-pack.gz.squashfs \
   ./emacs-geiser-guile.squashfs
$ singularity verify emacs-geiser-guile.squashfs
  WARNING: Authentication token file not found :
           Only pulls of public images will succeed
  Verifying image: emacs-geiser-guile.squashfs
           ERROR:   verification failed: failed to load SIF container file:
           invalid SIF file: Magic |'H��| want |SIF_MAGIC|
$ singularity shell emacs-geiser-guile.squashfs
  WARNING: passwd file doesn't exist in container, not updating
  WARNING: group file doesn't exist in container, not updating
  FATAL:   no /bin/sh found inside container

emacs-geiser-guile.squashfs is just squashfs but not container for singularity.

guix manual about guix pack described as follows,

   Yet another option is to produce a SquashFS image with the following
command:

     guix pack -f squashfs guile emacs geiser

The result is a SquashFS file system image that can either be mounted or
directly be used as a file system container image with the Singularity
container execution environment (http://singularity.lbl.gov), using
commands like ‘singularity shell’ or ‘singularity exec’.

Is above description is for version 2.6.1 but not 3.0?