Remove user from group

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 ~]$