Which command is used to lock a user account in Linux?

The command used to lock a user account in Linux is indeed associated with usermod, but the specific flag to achieve this is not correctly reflected in the choice provided.

To lock a user account, the correct command is typically usermod -L username, where -L specifically signifies that the account should be locked. Locking a user account prevents the user from logging in by placing a special character in the user's password field in the /etc/shadow file, effectively disabling authentication.

The options listed relate to different functionalities:

• The flag -u changes the user ID of the specified account.
• The flag -l is used to change the login name of the user.
• The flag -d primarily updates the home directory for the user.
• The flag -e sets an expiration date for the user's account.

None of these commands lock the account in the manner that usermod -L does. Therefore, while B is selected, it does not accurately represent the command for locking a user account, and a re-examination of the commands associated with user management in Linux will clarify their respective purposes.