Today I was surprised to ssh into my box running Arch Linux and find that /run/user/$(id -u) didn't exist.
The XDG Base Directory Specification says:
$XDG_RUNTIME_DIRdefines the base directory relative to which user-specific non-essential runtime files and other file objects (such as sockets, named pipes, …) should be stored. The directory MUST be owned by the user, and he MUST be the only one having read and write access to it. Its Unix access mode MUST be0700.The lifetime of the directory MUST be bound to the user being logged in. It MUST be created when the user first logs in and if the user fully logs out the directory MUST be removed. If the user logs in more than once he should get pointed to the same directory, and it is mandatory that the directory continues to exist from his first login to his last logout on the system, and not removed in between. Files in the directory MUST not survive reboot or a full logout/login cycle.
On a systemd box, is /run/user/$(id -u) the preferred place for $XDG_RUNTIME_DIR (even if it needs to be created?)
If not, what's best practice for creating $XDG_RUNTIME_DIR?
How do I ensure that that the directory is deleted only when I have "fully" logged out?
(Does "fully" mean that mean all processes created by login shells have exited? How to check for that?)
Best Answer
The
/run/user/Ndirectory, theuser@Nservice, and theXDG_RUNTIME_DIRenvironment variable are managed by a systemd-specific Pluggable Authentication Module and thelogindservice. On first log-on they create the directory, create the filesystem mounted there, and start the service; and on last log-off they stop the service, unmount the filesystem, and remove the directory. This behaviour changes when systemd'slingeroption is set for the account.Other systems operate differently.
Further reading
pam_systemd. systemd manual pages. Freedesktop.org.