Practice until you can't make it wrong.
Practice until you can't make it wrong.
Arch Linux
Removing user postfix from group opendkim
[tuyen@1 ~]$ which gpasswd /usr/bin/gpasswd [tuyen@1 ~]$ gpasswd -d postfix opendkim gpasswd: Permission denied. [tuyen@1 ~]$ sudo gpasswd -d postfix opendkim [sudo] password for tuyen: Removing user postfix from group opendkim [tuyen@1 ~]$