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.
The user is responsible for ensuring that the RUNTIME_DIR_PARENT directory
(/run/user by default) exists and is only writable by root.
To enable the pam module, add the following recommended configuration to
/etc/pam.d/system-login:
session optional pam_dumb_runtime_dir.so
See also pam.conf(5).
dumb_runtime_dir is released under the Zero Clause BSD license.