tmpfilesd

tmpfilesd is a daemon that participates in the systemd project to manage temporary files and runtime directories according to the tmpfiles.d configuration mechanism. It reads configuration files located in /usr/lib/tmpfiles.d, /run/tmpfiles.d, and /etc/tmpfiles.d and applies a set of actions at boot and, when requested, during system operation. The primary purpose is to ensure area like /tmp and /var/tmp exist with correct permissions and ownership, and to prevent accumulation of obsolete temporary files.

Configuration is provided through plain-text entries in .conf files. Each line typically specifies a path, a type (for example directory, file, symlink, or device node), a mode (permissions), an owner, a group, and optional age or argument fields. Common tasks include creating necessary directories with the right ownership and modes, adjusting file and directory permissions, removing files older than a configured age, and creating or linking files as needed. The syntax supports overrides from admin-provided files in /etc/tmpfiles.d while preserving distribution defaults in /usr/lib/tmpfiles.d.

tmpfilesd is usually invoked indirectly as part of the system startup sequence via systemd services such as systemd-tmpfiles-setup.service. It may also be triggered manually or by distribution-specific tooling to refresh or enforce the configured state of temporary and runtime files.

Security considerations include restricting operations to appropriate paths, avoiding risky changes in sensitive directories, and ensuring that automatic cleanup does not remove necessary runtime files. tmpfilesd thus provides a centralized, automated mechanism to maintain a clean and predictable filesystem state for temporary and runtime data.

See also: systemd, systemd-tmpfiles, tmpfiles.d.