Check correct syntax and file format of ‘/etc/group’ and groups existence

grpck

Create a new user belongs “admin” group called ‘user1′

useradd -c "Name Surname " -g admin -d /home/user1 -s /bin/bash user1

There is a simpler command too…

useradd user1

Rename a group

groupmod -n new_group_name old_group_name