systemd defaulting to tmpfs for /tmp causes enospc errors

[Paride Legovini]

Debian systemd now mounts a tmpfs on /tmp by default; relevant d/changelog entry:

systemd (256~rc3-3) unstable; urgency=medium

   * Make /tmp/ a tmpfs by default. Restore the upstream default and make
    /tmp/ a tmpfs. Can be overridden with: touch
    /etc/systemd/system/tmp.mount or: systemctl mask tmp.mount

Ubuntu is aligning to this, however this means that available space under /tmp is limited to the half of the available ram. That is sometimes not enough to unpack source trees in /tmp, see for example [1].

We need to to decide how to deal with this. Possibilities I can think about:

1. Disable the tmpfs tmp.mount, as suggested in the d/changelog entry. To be done in setup-testbed. Good: easy. Bad: deviates from the Ubuntu defaults, requires rebuilding the images.

2. Make autopkgtest use /var/tmp. Good: we stick to the defaults: Bad: requires non trivial changes in src:autopkgtest, which makes assumptions on stuff being in /tmp, on /tmp being cleared on reboots, ...

This under the assumption that the switch to a tmpfs has been discussed, and we want it in Ubuntu.

[1] https://autopkgtest.ubuntu.com/results/autopkgtest-oracular/oracular/ppc64el/c/ceph/20240618_194813_d6efc@/log.gz

[Nick Rosbrook (enr0n)]

I think option (2) is the probably the "best" fix. Another alternative I can think of is shipping a tmp.mount drop-in on the autopkgtest environment to change the size to something better. E.g.,

# /etc/systemd/system/tmp.mount.d/size.conf
[Mount]
Options=size=<param>

where <param> could be a percentage of RAM (e.g. 75%%), or an explicit size (e.g. 4GB). But then again, these defaults are intentionally easy to override. If the autopkgtest environment wants to do something different, I don't think it's the end of the world, and masking tmp.mount as a first step is fine.

> This under the assumption that the switch to a tmpfs has been discussed, and we want it in Ubuntu.

This was discussed in the foundations team, and the initial consensus was to not deviate from upstream and Debian.

[Paride Legovini (paride)]

This is affecting testing of the kernel packages (linux / linux-*), as those are tested with all-proposed (they're a special case in the autopkgtest-cloud worker script), and thus the new systemd is pulled in.

[Paride Legovini (paride)]

This implements option (1): https://salsa.debian.org/ci-team/autopkgtest/-/merge_requests/362

[Nick Rosbrook (enr0n)]

My understanding is that we will leave the systemd defaults as-is for now, so marking won't fix for systemd.

[Nick Rosbrook (enr0n)]

Actually, re-opening for systemd for now so it shows up on update-excuse.

[Launchpad Janitor (janitor)]

This bug was fixed in the package autopkgtest - 5.37ubuntu2

---------------
autopkgtest (5.37ubuntu2) oracular; urgency=medium

  * New delta, all upstream cherry-picks:
    - t/autopkgtest-build-docker: use ports.ubuntu.com on non-amd64 Ubuntu
    - t/autopkgtest: test_git_source_build: skip if remote repo is unreachable
    - d/t/lxd: restrict architectures via Architecture and enable arm64
    - d/rules: don't run pre-commit at package build time

 -- Paride Legovini <email address hidden> Wed, 26 Jun 2024 13:16:53 +0200