XDG_RUNTIME_DIR set to a non-existing directory in sbuild

[Michał Sawicz]

Starting yesterday we started seeing failures in different builds in a PPA:

https://launchpad.net/~mir-team/+archive/ubuntu/dev/+build/23237481

I tracked it down to `XDG_RUNTIME_DIR` being set to `/run/user/$UID` all of a sudden. Some other variables also got set (comparison against a working build):

 APT_CONFIG=/var/lib/sbuild/apt.conf
+DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/2001/bus
 DEB_BUILD_OPTIONS=parallel=4
 HOME=/sbuild-nonexistent
 LANG=C.UTF-8
@@ -20,3 +21,7 @@
 TERM=unknown
 USER=buildd
 V=1
+XDG_RUNTIME_DIR=/run/user/2001
+XDG_SESSION_CLASS=background
+XDG_SESSION_ID=c81
+XDG_SESSION_TYPE=unspecified

[Colin Watson (cjwatson)]

This is extremely strange, and seems to be non-deterministic: different builders booted using the same VM image end up with different variables visible in launchpad-buildd's environment. My best guess is that the environment set up by su(1) is sensitive to some other bit of the boot process and thus causes launchpad-buildd's environment to vary depending on when it's started.

The simplest way to fix this may be to convert launchpad-buildd from an init script to a systemd service, since it's usually easier to control its environment that way: in particular, su(1) would no longer need to be involved.

[Colin Watson (cjwatson)]

Switching launchpad-buildd to a systemd service hasn't made this go away, unfortunately. On the other hand, I do seem to be able to reproduce this every time on dogfood (or at least six out of my last six builds), so I might be able to make headway there since I can SSH into those builders. I didn't make much progress figuring it out tonight, but I need sleep, so maybe I'll spot something with fresh eyes.

My next plan is to upload a package with a "sleep $lots" in its build process, which would allow me to get in and see exactly which bit of the process tree is setting these environment variables. I think it may be libpam_systemd via schroot, but I'm not certain.

[Colin Watson (cjwatson)]

This turns out to be an schroot bug. See https://bugs.debian.org/898949.

[Launchpad Janitor (janitor)]

This bug was fixed in the package schroot - 1.6.10-12ubuntu3

---------------
schroot (1.6.10-12ubuntu3) jammy; urgency=medium

  * Don't create a logind session (closes: #898949, LP: #1964615).

 -- Colin Watson <email address hidden> Wed, 16 Mar 2022 15:30:36 +0000

[Colin Watson (cjwatson)]

We've deployed a cherry-pick of the schroot fix to focal.