I am currently using Ubuntu 18.04, and my username is abcxyz (not real, changed for the matter of the question). If I look at the contents of
/etc/groups, my user appears in many groups:
$ cat /etc/group | grep abcxyz adm:x:4:syslog,abcxyz,admin cdrom:x:24:abcxyz sudo:x:27:abcxyz,admin dip:x:30:abcxyz plugdev:x:46:abcxyz lpadmin:x:113:abcxyz,admin abcxyz:x:1000: sambashare:x:128:abcxyz,admin libvirtd:x:134:abcxyz,admin libvirt:x:134:abcxyz,admin docker:x:1002:abcxyz
However, when I execute
groups as my user, I only see:
$ groups abcxyz
I have already logout and logged back in, restarted computer, and try modifying the group the user belongs to with
usermod -a -G, but nothing seems to work.