Group administration
– Use the groupadd command to add a new group :
# groupadd [options] group_name
– Use the groupmod command to modify an existing group :
# groupmod [options] group_name
– Use groupdel to delete the group. You can remove a group even if there are users in the group. But you can not remove the primary group of an existing user. You must remove the user before removing the group.
# groupdel group_name
– Use the gpasswd command to administer the groups :
# gpasswd [options] group_name
For example : to add user test in group student –
# gpasswd -a test student
groups command
The groups command displays the group the user belongs to. For example the user oracle as shown below belongs to multiple groups which can be displayed using the groups command :
# groups oracle oracle : oinstall dba asm asmdba oper # grep oracle /etc/group oinstall:x:5004:oracle dba:x:5005:oracle asm:x:5006:oracle asmdba:x:5007:oracle oper:x:5008:oracle
newgrp command
The newgroup command executes a new shell and changes a user’s real group information. For example,
Before executing newgrp command
$ id uid=5004(oracle) gid=5004(oinstall) groups=5004(oinstall),5005(dba) ...
$ ps PID TTY TIME CMD 106591 pts/0 00:00:00 bash 106672 pts/0 00:00:00 ps
After executing newgrp command
$ newgrp dba
Note the gid for the user has changed to that of the student group :
$ id uid=5004(oracle) gid=5005(dba) groups=5005(dba),5004(oinstall) ...
Also note that a new shell has been executed.
$ ps PID TTY TIME CMD 106591 pts/0 00:00:00 bash 106231 pts/0 00:00:00 bash 106672 pts/0 00:00:00 ps