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.rosbr...@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.ca...@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 > > -- > ubuntu-devel mailing list > ubuntu-devel@lists.ubuntu.com > Modify settings or unsubscribe at: > https://lists.ubuntu.com/mailman/listinfo/ubuntu-devel >
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