Creating an XDG_RUNTIME_DIR

This article discusses the creation of an XDG_RUNTIME_DIR, a runtime directory used by applications for inter-component communication and storing runtime files. It reviews prior art such as dumb_runtime_dir, pam_rundir, pam_systemd, and simple but insecure methods like mkdir /tmp/run-$UID. The author outlines requirements, including sharing the same directory across concurrent user sessions, and evaluates various approaches: PAM model, setuid/setgid binaries, deterministic locations in /tmp, home directory storage, dedicated daemons, and randomized locations in /tmp. The preferred solution uses a non-deterministic location in /tmp with a lock file in $HOME to ensure security and coordination. This is a technical guide relevant to Linux system administration and IT/technology.