How do you lock a user account in Linux?

Locking a user account in Linux is typically accomplished through the use of the passwd command with the -l option. This command effectively disables the user’s password, which prevents the user from logging in. When you lock a user account with passwd -l username, the system modifies the user's password in the /etc/shadow file, prepending it with an exclamation mark (or similar character), which indicates that the account is locked. The account can be unlocked later with the corresponding passwd -u username command.

The other options listed do not perform the account locking function as effectively or correctly within standard Linux systems.