by using this command we can get groups under that username
groups linux
no username is passed then this command will display group membership for the current user
$ groups
it id of linux group
$ id linux
it gives all the group names
$ id -ng
by using this we can get the list of all groups
getent groups
print the first field containg the group name
$getent group| awk -F: '{print $1}'
cuts the first filed and displays only the group name
$ getent group cut -d: -f1