Re: Symlinks in "guix pack" and "guix shell"

[Tomas Volf]

On 2024-01-29 10:30:21 +0100, Konrad Hinsen wrote:
> Dear Guix experts,
>
> I am seeing inconsistent behavior with the creation of symbolic links
> in containers and exports, and I wonder whether this is a bug or missing
> documentation.
>
> According to the documentation, there are no constraints on what I can
> link to. In practice, some symbolic link requests have no effect, but
> there is no error message either.

That is interesting, at least in the guix shell case, I do get an error:

    $ guix shell -S /etc/ssl=etc/ssl -C bash coreutils -- ls -l /etc
    Backtrace:
    In guix/ui.scm:
      2287:10 19 (run-guix-command _ . _)
    In ice-9/boot-9.scm:
      1752:10 18 (with-exception-handler _ _ #:unwind? _ # _)
    In guix/store.scm:
        674:3 17 (guix-environment* _)
    In ice-9/boot-9.scm:
      1752:10 16 (with-exception-handler _ _ #:unwind? _ # _)
    In guix/store.scm:
       661:37 15 (thunk)
       1300:8 14 (call-with-build-handler _ _)
       1300:8 13 (call-with-build-handler #<procedure 7f3c6eb4e6f0 at g…> …)
    In guix/status.scm:
        839:4 12 (call-with-status-report _ _)
    In guix/scripts/environment.scm:
      1162:11 11 (_)
    In guix/store.scm:
      2180:25 10 (run-with-store #<store-connection 256.99 7f3c6dc21d70> …)
    In guix/scripts/environment.scm:
        873:8  9 (_ _)
    In gnu/build/linux-container.scm:
       397:16  8 (call-with-container (#<<file-system> device: "none…> …) …)
       265:16  7 (run-container _ _ (cgroup mnt pid ipc uts user net) _ # …)
    In guix/scripts/environment.scm:
       903:14  6 (_)
    In srfi/srfi-1.scm:
        634:9  5 (for-each #<procedure 7f3c7f64ecc0 at guix/scripts/env…> …)
    In ice-9/boot-9.scm:
      1747:15  4 (with-exception-handler #<procedure 7f3c6afeca80 at ic…> …)
      1747:15  3 (with-exception-handler #<procedure 7f3c6afeca20 at ic…> …)
    In gnu/build/install.scm:
       108:23  2 (_)
    In ice-9/boot-9.scm:
      1685:16  1 (raise-exception _ #:continuable? _)
      1685:16  0 (raise-exception _ #:continuable? _)

    ice-9/boot-9.scm:1685:16: In procedure raise-exception:
    symlink `.//etc/ssl' points to nonexistent file 
`/gnu/store/kxvplpa4c0xf5pap6br8abip2bq9f0p8-profile/etc/ssl'

>
> Example: I am trying to tell programs in a container to use the
> certificates from package nss-certs, instead of requiring the user
> to share /etc/ssl from the host machine. So I add
>
>    -S /etc/ssl=etc/ssl
>
> to my command lines for "guix shell -C" and "guix pack" (for creating
> Docker or Singularity images.
>
> Sometimes this works, sometimes it doesn't. With "guix shell", I never
> got it to work. With "guix pack", the observed behavior is random.
> Adding a completely unrelated package to my container can make the
> difference.

I think the relevant part is whether some certificate package is installed (via
propagated inputs) or not.  If I explicitly add nss-certs to the command above,
it starts to work:

    $ guix shell -S /etc/ssl=etc/ssl -C bash coreutils nss-certs -- ls -l /etc
    total 12
    -rw-r--r-- 1 wolf users 32 Jan 29 11:14 group
    -rw------- 1 wolf users 20 Jan 29 11:14 hosts
    -rw-r--r-- 1 wolf users 92 Jan 29 11:14 passwd
    lrwxrwxrwx 1 wolf users 59 Jan 29 11:14 ssl -> 
/gnu/store/s0mdc10pkb9kcmnzjfywax1d42rm4car-profile/etc/ssl

Could you please share some examples where you get no error, but it has no
effect?  Maybe they really are bugs (and should be reported).

Have a nice day,
Tomas Volf

--
There are only two hard things in Computer Science:
cache invalidation, naming things and off-by-one errors.

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