Once the account expiration date set using the chage command is reached, the user cannot log in to the system interactively. Some parameters of the chage command can be set using useradd and usermod. The usermod command can be used to lock an account with the -L option as shown in follows command line:

# usermod -L jack
# su - jack

We can also unlock the user account using the -U option as shown in the following command line:

# usermod -U jack