Cheatsheet & Examples: usermod

Cheatsheet & Examples: usermod

The usermod command modifies a user account's properties on a Linux system. It allows administrators to change various attributes associated with a user, such as the user's login name, home directory, shell, groups, and password expiry information.

Example Usage: usermod -l new_username old_username

What it does: Changes the user's login name from old_username to new_username.

Command-line Arguments Explained:

-l new_username: Specifies the new login name for the user.
old_username: Specifies the existing username whose login name needs to be changed.

Modifying User's Home Directory

Example Usage: usermod -d /new/home/directory username

What it does: Changes the user's home directory to the specified path.

Command-line Arguments Explained:

-d /new/home/directory: Sets the new home directory path for the user.
username: Specifies the username whose home directory is being modified.

Changing User's Primary Group

Example Usage: usermod -g groupname username

What it does: Changes the user's primary group to the specified group.

Command-line Arguments Explained:

-g groupname: Specifies the new primary group by its group name.
username: Specifies the username to modify.

Adding a User to Supplementary Groups

Example Usage: usermod -a -G group1,group2 username

What it does: Adds the user to the specified supplementary groups without removing them from their existing groups.

Command-line Arguments Explained:

-a: Appends the user to the supplementary group list. Requires the -G option.
-G group1,group2: Specifies a comma-separated list of group names to add the user to.
username: Specifies the username to modify.

Changing User's Shell

Example Usage: usermod -s /bin/bash username

What it does: Changes the user's default shell to the specified shell.

Command-line Arguments Explained:

-s /bin/bash: Sets the user's login shell (e.g., /bin/bash, /bin/zsh).
username: Specifies the username to modify.

Locking and Unlocking a User Account

Example Usage: usermod -L username (Lock) usermod -U username (Unlock)

What it does: Locks or unlocks a user account, preventing or allowing login.

Command-line Arguments Explained:

-L: Locks the user's password, effectively disabling login by prefixing the password hash in /etc/shadow with !.
-U: Unlocks the user's password by removing the ! from the password hash in /etc/shadow, enabling login.
username: Specifies the username to modify.

Setting Password Expiration Information

Example Usage: usermod -e YYYY-MM-DD username

What it does: Sets the date after which the user's password will expire.

Command-line Arguments Explained:

-e YYYY-MM-DD: Sets the account expiration date. Use YYYY-MM-DD format.
username: Specifies the username to modify.

Modifying User's UID and GID

Example Usage: usermod -u 1001 username usermod -g 1002 username

What it does: Changes the user's User ID (UID) and Group ID (GID).

Command-line Arguments Explained:

-u 1001: Changes the user's UID to 1001. This needs to be a unique ID.
-g 1002: Changes the user's GID to 1002. This should match an existing group ID.
username: Specifies the username to modify.