Comment by nybble41

Right, /var/tmp is the "Persistent Temp" directory, and /tmp is "Ephemeral Temp". The /run directory is for runtime data such as PID files, Unix sockets, named FIFOs, and generated systemd units—it has a specific internal structure and shouldn't be used as a direct alternative to the relatively unstructured /tmp directory. While both are generally ephemeral tmpfs mounts, only /tmp is writable to all users.