how to create a group in linux

Users can be listed in groups. Groups allow you to set permissions on the group level instead of having to set permissions for every individual user. Every Unix or Linux distribution will have a graphical tool to manage groups. Novice users are advised to use this graphical tool. More experienced users can use command line tools to manage users.

groupadd

Groups can be created with the groupadd command. The example below shows the

creation of five (empty) groups.

root@linux:~# groupadd tennis

root@linux:~# groupadd football

root@linux:~# groupadd snooker

root@linux:~# groupadd formula1

root@linux:~# groupadd salsa

/etc/group

Users can be a member of several groups. Group membership is defined by the /etc/group file.

root@linux:~# tail  -5  /etc/group

tennis:x:1006:

football:x:1007:

snooker:x:1008:

formula1:x:1009:

salsa:x:1010:

root@linux:~#

The first field is the group's name. The second field is the group's (encrypted) password (can be empty). The third field is the group identification or GID. The fourth field is the list of members, these groups have no members.

usermod

Group membership can be modified with the useradd or usermod command.

root@linux:~# usermod -a -G tennis inge

root@linux:~# usermod -a -G tennis katrien

root@linux:~# usermod -a -G salsa katrien

root@linux:~# usermod -a -G snooker sandra

root@linux:~# usermod -a -G formula1 annelies

root@linux:~# tail -5 /etc/group

tennis:x:1006:inge,katrien

football:x:1007:

snooker:x:1008:sandra

formula1:x:1009:annelies

salsa:x:1010:katrien

root@linux:~#

Be careful when using usermod to add users to groups. By default, the usermod command will remove the user from every group of which he is a member if the group is not listed in the command! Using the -a (append) switch prevents this behaviour.

groupmod

You can change the group name with the groupmod command.

root@linux:~# groupmod -n darts snooker

root@linux:~# tail -5 /etc/group

tennis:x:1006:inge,katrien

football:x:1007:

formula1:x:1009:annelies

salsa:x:1010:katrien

darts:x:1008:Sandra

groupdel

You can permanently remove a group with the groupdel command.

root@linux:~# groupdel tennis

root@linux:~#

groups

A user can type the groups command to see a list of groups where the user belongs to.

[harry@Linux ~]$ groups

harry sports

[harry@Linux ~]$

gpasswd

You can delegate control of group membership to another user with the gpasswd command. In the example below we delegate permissions to add and remove group members to serena for the sports group. Then we su to serena and add harry to the sports group.

[root@Linux ~]# gpasswd -A serena sports

[root@Linux ~]# su - serena

[serena@Linux ~]$ id harry

uid=516(harry) gid=520(harry) groups=520(harry)

[serena@Linux ~]$ gpasswd -a harry sports

Adding user harry to group sports

[serena@Linux ~]$ id harry

uid=516(harry) gid=520(harry) groups=520(harry),522(sports)

[serena@Linux ~]$ tail -1 /etc/group

sports:x:522:serena,venus,harry

[serena@Linux ~]$

Group administrators do not have to be a member of the group. They can remove themselves from a group, but this does not influence their ability to add or remove members.

[serena@Linux ~]$ gpasswd -d serena sports

Removing user serena from group sports

[serena@Linux ~]$ exit

Information about group administrators is kept in the /etc/gshadow file.

[root@Linux ~]# tail -1 /etc/gshadow

sports:!:serena:venus,harry

[root@Linux ~]#

To remove all group administrators from a group, use the gpasswd command to set an empty administrators list.

[root@Linux ~]# gpasswd -A "" sports