Debian's /tmpest in a teapot
By now, using tmpfs for the /tmp directory is a road well-traveled. Many Linux distributions have already switched to mounting /tmp as a tmpfs. Arch Linux, Fedora, openSUSE Tumbleweed, and many others have all made the switch. Red Hat Enterprise Linux (RHEL) and its clones, as well as SUSE Linux Enterprise Server (SLES) and openSUSE Leap, still default to /tmp on disk. Ubuntu, following Debian, also continues to have a disk-based /tmp rather than using tmpfs.
The knobs to control how /tmp is mounted, and the handling of temporary files, are part of systemd. (On systems where systemd is used, of course.) The upstream defaults for systemd are to mount /tmp as a tmpfs and delete files that have not been read or changed after ten days in /tmp and 30 days for those stored in /var/tmp. Debian Developer and systemd contributor Luca Boccassi recently decided it was time to revisit the topic of /tmp as a tmpfs, and start deleting temporary files in /tmp and /var/tmp.
On May 6 Boccassi resurrected a discussion from Debian's bug tracker that started in 2020 and that had trailed off in July 2022 without resolution. The bug was submitted by Eric Desrochers, who complained that Debian's systemd implementation did not clean /var/tmp by default. Michael Biebl wrote that this was a deliberate choice to match Debian's pre-systemd behavior. After a long period of inactivity, Biebl suggested in October 2021 (and again in July 2022) that Desrochers raise the topic on the Debian devel mailing list. That never happened.