Search for files and processes owned by the user.
To lock their password, preventing login via password: passwd -l username.
To expire the account, disabling authentication of any kind: chage -E 0 username or usermod -e 0 username.
Archive the home directory, crontab, and mail: tar czf /home/username.tgz /home/username /var/spool/cron/username /var/spool/mail/username.
Check for running processes owned by user: ps -fp $(pgrep -u username).
If user’s processes need to be killed: killall -KILL -u username.
Delete the user account and home directory: userdel -r username.
To see what’s configured to be created for new users and deleted when running the userdel command, see /etc/login.defs.
See also: