display current group names
' groups 'u groups [ user ]
The groups command displays the current group names or ID values . If the value does not have a corresponding entry in /etc/group, the value will be displayed as the numerical group value . The optional user parameter will display the groups for the named user .
Systems which do not support concurrent group sets will have the information from /etc/group reported . The user must use newgrp or sg to change his current real and effective group ID .
/etc/group Group account information .
newgrp(1), getgid(2), getgroups(2), getuid(2).