How to: linux add user to group

Recheck using below command:

[root@rhel1 ~]# id foo
uid=511(foo) gid=511(foo) groups=511(foo),509(sales)
[root@rhel1 ~]#

Above output confirms that sales is the secondary group whereas primary group is foo only.

• Linux add user to group while creating user with multiple secondary groups.

You can specify multiple secondary group using comma while creating the user itself in useradd command.

[root@rhel1 ~]# useradd -G sales,accounts,marketing bar

Confirm using below command:

[root@rhel1 ~]# id bar
uid=512(bar) gid=513(bar) groups=513(bar),509(sales),510(accounts),512(marketing)
[root@rhel1 ~]#

Also there is one more way for confirmation:

[root@rhel1 ~]# cat /etc/group|grep bar
sales:x:509:foo,bar
accounts:x:510:bar
marketing:x:512:bar
bar:x:513:
[root@rhel1 ~]#

• Linux add user to group for existing user.

You can also change secondary group for existing users using “-G” option for usermod command. Let’s say you want to change the secondary group of the user foo from sales to accounts.

[root@rhel1 ~]# usermod -G accounts foo
[root@rhel1 ~]# id foo
uid=511(foo) gid=511(foo) groups=511(foo),510(accounts)
[root@rhel1 ~]#

In case you want to add one more secondary group instead of changing it as above then you must use “-a” (append) option.

[root@rhel1 ~]# usermod -a -G marketing foo
[root@rhel1 ~]# id foo
uid=511(foo) gid=511(foo) groups=511(foo),510(accounts),512(marketing)
[root@rhel1 ~]#

• Linux add user to group for existing user with multiple secondary groups.

You can specify multiple secondary groups using comma for existing user with command in usermod command.

[root@rhel1 ~]# usermod -a -G sales,hr foo
[root@rhel1 ~]# id foo
uid=511(foo) gid=511(foo) groups=511(foo),509(sales),510(accounts),512(marketing),514(hr)
[root@rhel1 ~]#

In case you don’t specify -a option then current secondary groups will be flushed and replaced by specified group names.

[root@rhel1 ~]# id foo
uid=511(foo) gid=511(foo) groups=511(foo),509(sales),510(accounts),512(marketing),514(hr)
[root@rhel1 ~]# usermod -G sales,hr foo
[root@rhel1 ~]# id foo
uid=511(foo) gid=511(foo) groups=511(foo),509(sales),514(hr)
[root@rhel1 ~]#

NOTE:So make sure you use -a option incase you want to append to existing group instead of changing the existing secondary groups.