Substitutes a literal GID UID with the UID GID of the current owner of the process.
execl-subuidgid [ -o owner ] prog
UID
GID
on prog.UID
GID
of owner instead of the current one. execl-subuidgid
if { mkdir -p /run/user }
chown -R $UID:$GID /run/user
execl-subuidgid -o root
if { mkdir /run }
chmow -R $UID:$GID /run/user