Bug#1084133: mutter: FTBFS on armhf: Directory "/tmp/.X11-unix" is not writable

[Simon McVittie]

Source: mutter
Version: 47.0-2
Severity: serious
Tags: ftbfs
Justification: fails to build from source (but built successfully in the past)
X-Debbugs-Cc: debian-arm at lists.debian.org, armhf at buildd.debian.org
User: debian-arm at lists.debian.org
Usertags: armhf
Control: block 1081519 by -1

The recent upload of mutter in unstable FTBFS on multiple armhf buildds:
arm-ubc-01, arm-conova-03, arm-ubc-05. Interestingly, the arm64 build on
one of the same buildds (arm-conova-03) was successful.

The error message suggests that there might be a problem with the
chroot/container, or possibly with the host /tmp being shared with it:

> Bail out! libmutter-FATAL-ERROR: Failed to start X Wayland: Directory "/tmp/.X11-unix" is not writable

Please could a buildd operator check whether something is not working
as intended on these buildds?

Ideally, mutter's build-dependencies would ensure that /tmp/.X11-unix is
created with its canonical ownership and permissions (1777 root:root),
but invocation of /etc/init.d/x11-common is suppressed in a chroot, and
systemd's /usr/lib/tmpfiles.d/x11.conf only creates /tmp/.X11-unix during
boot (and not when systemd is installed into a running system). Possibly
this directory is sufficiently special that schroot and unshare ought
to ensure its presence as an empty directory with the correct permissions
during chroot setup, but that can be a separate feature request.

The affected buildds seem to be using schroot, as opposed to unshare.
I don't know precisely how it is configured (/tmp from the host, or
/tmp part of the chroot, or what).

Thanks,
    smcv