Hello Nick,
Mounting /tmp as tmpfs makes sense on systems that are not very memory constrained. I have been using this for the last years on all my systems.
I am wondering which mount option shall be used. I have tended to mount with nosuid,nodev. But there are some rare use cases, e.g. with chroots where this runs into issues.
Best regards
Heinrich
On Wed, May 21, 2025 at 4:20 PM Nick Rosbrook <nick.rosbrook@canonical.com> wrote:
Hi,
### Background
In the 24.10 cycle, Ubuntu began defaulting to /tmp as a tmpfs
(interestingly, Ubuntu was poised to do this many releases ago[1], but
apparently did not go through with it at the time), and /var/tmp being
cleaned up on a timer. This was done at the same time as Debian[2],
and aligns both Debian and Ubuntu with upstream systemd. To summarize
the changes:
1. /tmp became a tmpfs, with a cleanup age of 10d. Just like before,
/tmp is cleaned on reboot, and a cleanup time is enforced to remove
old/unused files. The primary difference is that instead of being a
directory on the rootfs, /tmp is its own tmpfs with default size of
50% RAM.
2. /var/tmp gained a cleanup age of 30d. /var/tmp is still part of the
rootfs, and is not cleaned on reboot.
3. Unlike Debian, we did not introduce a transitional
/etc/systemd/tmpfiles.d/tmp.conf on upgrades. This is due to Ubuntu's
stated goal to have consistency between upgraded and newly-installed
systems.
These changes are easy for a user/administrator to modify/override.
$ systemctl mask tmp.mount
or
$ touch /etc/systemd/system/tmp.mount
will prevent /tmp from being a tmpfs. And,
$ echo 'D /tmp 1777 root root 30d' > /etc/tmpfiles.d/tmp.conf
will restore the 24.04 LTS defaults for /tmp and /var/tmp cleanup ages
(the 30d cleanup age is relatively recent in Ubuntu[3]). See [4][5]
for comprehensive documentation on the configuration options.
### What now?
Overall, there has been little push back to this change. Mostly, I
have seen some expected complaints related to /tmp vs. /var/tmp usage.
However, I have heard enough anecdotes (conversations, DMs, etc.) from
Ubuntu developers that I thought it was worth bringing this up on
ubuntu-devel now. My questions are:
1. Does anyone have a strong reason for changing these defaults? This
would mean diverging from Debian and upstream.
2. Should we have a different transition plan for upgrades? In
particular for 24.04 LTS to 26.04 LTS?
Please keep in mind these are only defaults. As explained above, they
can be easily modified for special cases.
Thanks,
Nick
[1] https://ubuntu.com/blog/data-driven-analysis-tmp-on-tmpfs
[2] https://lwn.net/ml/debian-devel/ebee234c6f72eb7dfe55809821c038491bfea542.camel@debian.org/
[3] https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/2019026
[4] https://www.freedesktop.org/software/systemd/man/latest/tmpfiles.d.html
[5] https://www.freedesktop.org/software/systemd/man/latest/systemd.mount.html
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