usermod
On CentOS, the wheel group allows users in this group to run commands as user root with sudo.
To add a user to the wheel group, run
usermod -aG wheel USERNAME
On Ubuntu/Debian, use
usermod -aG sudo USERNAME
Remove a User from Group
deluser USERNAME GROUP
Example
root@ip-172-31-56-4:~# deluser designware sudo
Removing user `designware' from group `sudo' ...
Done.
root@ip-172-31-56-4:~#
Here we remove user designware from group sudo.
To remove a user from all secondary groups, run
usermod -G "" USERNAME
Change user shell
To disable SSH login, run
usermod -s /sbin/nologin USERNAME
For example
usermod -s /sbin/nologin mysql