bug#26809: 08/09: services: nscd: Create /etc/resolv.conf if it does not exist.

[Mark H Weaver <mhw@netris.org>]

ludo@gnu.org (Ludovic Courtès) writes:

> civodul pushed a commit to branch master
> in repository guix.
>
> commit 49f9d7f697d19870f01104cdb6a90a32aea87679
> Author: Ludovic Courtès <ludo@gnu.org>
> Date:   Tue May 2 12:21:31 2017 +0200
>
>     services: nscd: Create /etc/resolv.conf if it does not exist.
>     
>     * gnu/services/base.scm (nscd-activation): Create /etc/resolv.conf if it
>     does not exist yet.

This commit broke the boot process on my system.  The problem is that
I'm using Network Manager, which makes /etc/resolv.conf into a symlink
that points to /var/run/NetworkManager/resolv.conf.  Since /var/run is
cleaned during early boot, when this new activation code runs,
/etc/resolv.conf is a broken symlink.

I guess that 'file-exists?' returns #false for a broken symlink, and the
'call-with-output-file' tries to open the target of the symlink, which
fails.

       Mark


> diff --git a/gnu/services/base.scm b/gnu/services/base.scm
> index 67972bf..a64faa0 100644
> --- a/gnu/services/base.scm
> +++ b/gnu/services/base.scm
> @@ -1149,7 +1149,14 @@ the tty to run, among other things."
>    #~(begin
>        (use-modules (guix build utils))
>        (mkdir-p "/var/run/nscd")
> -      (mkdir-p "/var/db/nscd")))                  ;for the persistent cache
> +      (mkdir-p "/var/db/nscd")                    ;for the persistent cache
> +
> +      ;; In libc 2.25 nscd uses inotify to watch /etc/resolv.conf, but only if
> +      ;; that file exists when it is started.  Thus create it here.
> +      (unless (file-exists? "/etc/resolv.conf")
> +        (call-with-output-file "/etc/resolv.conf"
> +          (lambda (port)
> +            (display "# This is a placeholder.\n" port))))))
>  
>  (define nscd-service-type
>    (service-type (name 'nscd)