Subject: bug#71352: branch master updated: services: nix: Mount Nix store read only.

From: Maxim Cournoyer <[email-masked]>
Date: Mon, 03 Jun 2024 22:34:35 -0400

Hello,

[email-masked] writes:

>     services: nix: Mount Nix store read only.
>     
>     * gnu/services/nix.scm (nix-shepherd-service): Add requirements.
>     (%nix-store-directory): New variable.
>     (nix-service-type): Add file-system-service-type extension.
>     
>     Change-Id: I18a5d58c92c1f2b5b6dcecc3d5b439cc15bf4e49

This commit unfortunately appears to introduce a regression where
reconfiguring a system with the read-only /nix/store causes the
following error:

--8<---------------cut here---------------start------------->8---
guix system: error: chown: Système de fichiers accessible en lecture seulement
--8<---------------cut here---------------end--------------->8---

With the accompanying strace output:

--8<---------------cut here---------------start------------->8---
20261 close(17)                         = 0
20261 chown("/nix/store", 0, 981)       = -1 EROFS (Système de fichiers accessible en lecture seulement)
20261 close(13)                         = 0
20261 write(2, "guix system: \33[1;31merror: \33[0m\33[1mchown\33[0m: Syst\303\250me de fichiers accessible en lecture seulement\n", 99) = 99
--8<---------------cut here---------------end--------------->8---

Are these chown still useful in the activation snippet?

--8<---------------cut here---------------start------------->8---
(define (nix-activation _)
  ;; Return the activation gexp.
  #~(begin
      (use-modules (guix build utils)
                   (srfi srfi-26))
      (for-each (cut mkdir-p <>) '("/nix/store" "/nix/var/log"
                                   "/nix/var/nix/gcroots/per-user"
                                   "/nix/var/nix/profiles/per-user"))
      (chown "/nix/store"
             (passwd:uid (getpw "root")) (group:gid (getpw "nixbld01")))
      (chmod "/nix/store" #o775)
      (for-each (cut chmod <> #o777) '("/nix/var/nix/profiles"
                                       "/nix/var/nix/profiles/per-user"))))
--8<---------------cut here---------------end--------------->8---

If they are useful only on the first time, perhaps we could catch the
exceptions for when it runs on an already read-only mounted /nix/store?

-- 
Thanks,
Maxim