LFCS / reference

reference

useradd -m -s /bin/bash -G grp u

Create user w/ home, shell, group

usermod -aG grp u

Append user to group

usermod -L u / usermod -U u

Lock / unlock account

chage -M 90 -E 2026-12-31 u

Max age + expiry

passwd u

Set password

visudo -f /etc/sudoers.d/u

Safely edit a sudoers drop-in

chmod 750 f / chmod g+s d / chmod +t d

Octal / SGID / sticky

chown u:g f / chgrp g f

Change owner / group

setfacl -m u:carol:rwx f / getfacl f

Set / view ACL

setfacl -d -m u:carol:rwx d

Default (inherited) ACL

chattr +i f / lsattr f

Immutable bit / view attrs