group information is maintained in the kernel, and is accessible
via the file system hierarchy (beneath
<filename>/sys/fs/cgroup/systemd/</filename>), or in tools such as
+ <citerefentry project='man-pages'><refentrytitle>systemd-cgls</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+ or
<citerefentry project='man-pages'><refentrytitle>ps</refentrytitle><manvolnum>1</manvolnum></citerefentry>
(<command>ps xawf -eo pid,user,cgroup,args</command> is
particularly useful to list all processes and the systemd units