Linux User Password and Chage Command

Managing Linux User Passwords

In Linux, user passwords are managed using the passwd command. This command allows you to set or change a user's password securely.

Example:

sudo passwd username

This command prompts you to enter and confirm the new password for the specified user.

The /etc/shadow file contains password information for users. Each line in this file corresponds to a user and contains the following fields:

                username:password:last_change:min:max:warn:inactive:expire:reserved

Where:

username: The name of the user.
password: The hashed password (or a placeholder like 'x' or '*').
last_change: The last date the password was changed (in days since Jan 1, 1970).
min: The minimum number of days before a password can be changed.
max: The maximum number of days a password is valid.
warn: The number of days before expiration that a warning is given.
inactive: The number of days after expiration until the account is disabled.
expire: The date when the account will expire (in days since Jan 1, 1970).
reserved: Reserved for future use.

Option	Description
`-d`	Delete the password for the specified user.
`-e`	Expire the password immediately, forcing the user to change it on next login.
`-i`	Set the number of days after password expiration until the account is disabled.
`-l`	Lock the user's password, preventing login.
`-u`	Unlock the user's password, allowing login.
`-n`	Set the minimum number of days before a password can be changed.
`-x`	Set the maximum number of days a password is valid.
`-w`	Set the number of days before expiration that a warning is given.
`-y`	Set the number of days after expiration until the account is disabled.
`-f`	Set the number of days after password expiration until the account is disabled.
`-h`	Display help information for the command.
`-r`	Change the password for a user in the shadow file.
`-s`	Set the password for a user in the shadow file.

The chage command is used to manage password aging policies for a user. It allows you to set expiration dates, warning periods, and more.

chage [options] username

Option	Description
`-l`	Display the current password aging settings for a user.
`-M`	Set the maximum number of days a password is valid.
`-m`	Set the minimum number of days before a password can be changed.
`-W`	Set the number of days before expiration that a warning is given.
`-I`	Set the number of days after expiration until the account is disabled.
`-E`	Set the date when the account will expire.
`-h`	Display help information for the command.
`-r`	Change the password for a user in the shadow file.
`-s`	Set the password for a user in the shadow file.

Note: The chage command requires superuser privileges to modify password aging settings.

To set a password to expire after 90 days and give a warning 7 days before expiration:

sudo chage -M 90 -W 7 username

To view the current password aging settings for a user:

sudo chage -l username