How Do I Create an XDG_RUNTIME_DIR

2026-05-05

In Linux distributions without systemd (such as Void, Alpine, or Gentoo), configuring the XDG_RUNTIME_DIR environment variable is required for running Wayland compositors, PipeWire, and D-Bus user sessions.

The Freedesktop base directory specification mandates that this directory must be owned by the user (0700 permissions), created on login, removed on full logout, and must not survive a reboot.

I. User-Space and Scripting Solutions

These operate in the user's login shell. Due to privilege and phase limitations, they rarely meet the specification securely.

• Fixed Path Scripts (mkdir /tmp/run-$UID)

• Mechanism: Creates a directory in a globally writable path.

• Flaws: High security risk. Predictable paths allow malicious users to hijack the directory via symlinks or cause DoS.

• Random Paths & File Locks (mkrundir)

• Mechanism: Creates a randomized directory in /tmp and uses locks in $HOME to sync sessions.

• Flaws: Breaks graphical Display Managers (GDM/SDDM) because they bypass shell profiles. Causes issues if $HOME is shared over NFS.

II. System-Level and Session Management Solutions

These operate within the PAM stack using root privileges, resolving permission and DM compatibility issues.

• elogind

• Status: Fully compliant.

• Mechanism: Independent session manager extracted from systemd.

• Flaws: Heavy and maintains a hard dependency on D-Bus.

• turnstile

• Status: Fully compliant.

• Mechanism: A lightweight, modern PAM module + daemon solution that uses process-level reference counters.

• Flaws: Requires a permanent background daemon.

• pam_rundir

• Status: Fully compliant.

• Mechanism: A pure C PAM module using flock to maintain a hidden session counter.

• Flaws: Only tracks PAM login sessions. It is unaware of lingering processes like tmux or gpg-agent. When the last terminal closes, it runs rm -rf, deleting the runtime directory and severing the active UNIX sockets of your background tasks.

• pam_dumb_runtime_dir

• Status: Non-compliant.

• Mechanism: Creates the directory at /run/user/$UID with correct permissions upon login. It performs no cleanup on logout.

III. Conclusion and Final Selection

Considering security, complexity, and background process compatibility, pam_dumb_runtime_dir is my choice.

As the author states:

"Creates an XDG_RUNTIME_DIR directory on login per the freedesktop.org base directory spec. Flaunts the spec and never removes it, even after last logout. This keeps things simple and predictable."

Why this is acceptable:

1. Memory Management: /run is almost always a tmpfs (RAM-based filesystem). Although files persist after logout, they are wiped instantly upon reboot or power loss.
2. Safety: By refusing to clean up, it avoids the "murderous" behavior of pam_rundir, ensuring tmux sockets and background daemons remain accessible until the system shuts down.
3. Simplicity: It avoids background daemons, complex counting logic, and external dependencies.