file-hierarchy(7) states /dev/shm is tmpfs and that "all users have write access to this directory", so I think you'd have to be making a non-systemd distro
> Usually, it is a better idea to use memory mapped files in /run/ (for system programs) or $XDG_RUNTIME_DIR (for user programs) instead of POSIX shared memory segments, since these directories are not world-writable and hence not vulnerable to security-sensitive name clashes.
$XDG_RUNTIME_DIR usually points to /run/user/${uid}, so you're guaranteed that other users won't write there, and possibly won't even be able to read there.
