How to modify, lock, or delete a user in Linux

Change or remove a user account. Locking is reversible; deleting is not. Run as root.

Locking a user blocks login but keeps the account; userdel -r also removes the home directory and mail and cannot be undone. Prefer locking when in doubt, and check for files the user owns before deleting.

# Lock / unlock login
sudo usermod -L <user>
sudo usermod -U <user>

# Change the login shell (e.g. disable shell access)
sudo usermod -s /sbin/nologin <user>

# Delete the account only (keep the home directory)
sudo userdel <user>

# Delete the account AND its home + mail - irreversible
sudo userdel -r <user>

# Before deleting, find files the user owns
sudo find / -xdev -user <user> 2>/dev/null | head