Debian 13 now uses RAM as the storage for /tmp via tmpfs. It will use up to half of the available memory on the system.

There is a simple way to undo this and put /tmp back on disk. Doing so will remove any files that are currently in /tmp.

sudo systemctl mask tmp.mount

Then you need to restart your system

H/T – https://josephscott.org/blog/2025/how-to-switch-debian-13-tmp-from-tmpfs-to-disk/