From Wsms

Note: This page should be titled groups (all lowercase). It is Groups due to technical limitations of Mediawiki.

groups prints the groups a user is in.

Common Usage

As a user, list your group memberships:

[ggeller@arthur ~]$ groups
ggeller wheel

A root, list groups to which a user belongs

[root@arthur ~]# groups ggeller
ggeller : ggeller

see also

man groups
usermod