GROUPS(1)
NAME
groups − show group memberships
USAGE
groups [ user ]
DESCRIPTION
The groups command shows the groups to which you or the optionally specified user belong. Each user belongs to a group specified in the password file /etc/passwd, and possibly to other groups as specified in the file /etc/group. If you do not personally own a file, but belong to the group who owns it, then you are granted group access to the file.
When a new file is created, it is given the group of the containing directory.
FILES
/etc/passwd
/etc/group