[root@sanjeeb ~]# grep sanjeeb /etc/passwd
sanjeeb:x:1000:1000:Sanjeeb KC:/home/sanjeeb:/bin/bash
 
[root@sanjeeb ~]# grep sanjeeb /etc/group 
sanjeeb:x:1000:
 
[root@sanjeeb ~]# grep sanjeeb /etc/shadow 
sanjeeb:$6$8E/Bt1v3w03gU8O/$KAI7oPCnjbzZ8mhaHFGcIREWlaxzqNi1nxOg6cs5x09dGvciEZd8bSSiccWZUA5eBBQRRAzLg0cnp2FvtnZFV1::0:99999:7:::

[root@sanjeeb ~]# groupadd friends 
 
[root@sanjeeb ~]# grep friends /etc/group 
friends:x:1006:
 
# Creating group with id 
[root@sanjeeb ~]# groupadd -g 4000 family 
[root@sanjeeb ~]# grep family /etc/group 
family:x:4000:

# Modifying group name 
[root@sanjeeb ~]# groupmod -n newfriends friends 
[root@sanjeeb ~]# grep friends /etc/group 
newfriends:x:1006:
 
# Modifying group id
[root@sanjeeb /]# groupmod -g 1009 manager 
[root@sanjeeb /]# grep manager /etc/group 
manager:x:1009:

[root@sanjeeb ~]# groupdel newfriends 

[root@sanjeeb ~]# groupadd sales 
[root@sanjeeb ~]# groupadd marketing 
[root@sanjeeb ~]# groupadd production 
 
[root@sanjeeb ~]# egrep '(sales|marketing|production)' /etc/group 
sales:x:1001:
marketing:x:1002:
production:x:1003:
 
# To add user in group when creating user 
[root@sanjeeb ~]# useradd -G sales hanuman 
 
# To modify a user to add group 
[root@sanjeeb ~]# usermod -G marketing ram 
 
# To modify user in multiple groups 
[root@sanjeeb ~]# usermod -G marketing,sales,production bharat 
[root@sanjeeb ~]# egrep '(sales|marketing|production)' /etc/group 
sales:x:1001:hanuman,bharat
marketing:x:1002:ram,bharat
production:x:1003:bharat
 
# To append a user in another group 
[root@sanjeeb ~]# usermod -aG sales ram 
[root@sanjeeb ~]# grep sales /etc/group 
sales:x:1001:hanuman,bharat,ram