Because users group membership is defined in two different locations, it can be difficult to find out which groups exactly a user is a member of. A convenient command to check this is  groupmems . Use, for example, the command  groupmems -g sales -l  to see which users are a member of the group sales. This shows users who are a member of this group as a secondary group assignment, but also users who are a member of this group as the primary group assignment. 

[root@rhel7 ~]# groupmems --helpUsage: groupmems [options] [action]Options:  -g, --group groupname         change groupname instead of the user's group                                (root only)  -R, --root CHROOT_DIR         directory to chroot intoActions:  -a, --add username            add username to the members of the group  -d, --delete username         remove username from the members of the group  -h, --help                    display this help message and exit  -p, --purge                   purge all members from the group  -l, --list                    list the members of the group

例：

查看有哪些用户属于sales组

[root@rhel7 ~]# groupmems -g sales -llinda lisa

从sales组中删除lisa

[root@rhel7 ~]# groupmems -d lisa -g sales  [root@rhel7 ~]# groupmems -g sales -llinda

添加用户到组里

[root@rhel7 ~]# id lxj2uid=1002(lxj2) gid=0(root) groups=0(root)[root@rhel7 ~]# groupmems -a lxj2 -g sales[root@rhel7 ~]# id lxj2uid=1002(lxj2) gid=0(root) groups=0(root),1238(sales)

也可以使用usermod命令将用户添加到组里 

usermod -aG  will add users to new groups that will be used as their secondary group.

Use  usermod  to add users linda and lisa to the group sales, and lori and bob to the group account:    

usermod -aG sales linda  usermod -aG sales lisa  usermod -aG account lori  usermod -aG account bob