The usermod Command in Linux: Renaming, Groups, UID, and Shell

usermod is a utility for modifying the parameters of an existing user account. Unlike useradd (create) and userdel (delete), usermod works with already-created accounts and allows changing nearly any of their attributes without recreating them.

Root privileges are required. All changes are written directly to the system files /etc/passwd, /etc/shadow, and /etc/group.

Syntax

usermod [options] username

Rename a User

sudo usermod -l newusername oldusername

Changes only the login name. The home directory, UID, and file contents remain unchanged. To also rename the home folder, add -d with -m:

sudo usermod -l newusername -d /home/newusername -m oldusername

-m (move) physically moves the contents of the old home directory to the new one.

Change the Home Directory

Set a new path without moving files:

sudo usermod -d /new/home/dir username

Set a new path and move the files:

sudo usermod -d /new/home/dir -m username

Without -m, the new path is only recorded in /etc/passwd — it is not physically created or populated.

Add a User to a Group

Add to a supplementary group (without removing from current ones):

sudo usermod -aG groupname username

The -a (append) flag is required — without it the user is removed from all current groups and added only to the specified one.

Add to multiple groups at once:

sudo usermod -aG sudo,docker,www-data username

Check a user's current groups:

groups username

Or with more detail:

id username

Important: group changes take effect on the user's next login. New groups are not active in the current session. To apply without re-logging in: newgrp groupname.

Change the Primary Group

sudo usermod -g newgroupname username

Lowercase -g changes the primary group; uppercase -G changes the list of supplementary groups.

Change the User's UID

sudo usermod -u 1500 username

Automatically updates file ownership in the home directory. Files outside the home directory need to be updated manually:

find / -user old_uid -exec chown -h username {} \;

Make sure the new UID is not already taken:

grep 1500 /etc/passwd

Change the Login Shell

sudo usermod -s /bin/bash username

List available shells:

cat /etc/shells

Common options:

sudo usermod -s /bin/zsh username         # zsh
sudo usermod -s /bin/sh username          # sh (minimal)
sudo usermod -s /usr/bin/fish username    # fish
sudo usermod -s /sbin/nologin username    # block shell login

/sbin/nologin is a convenient way to create a system user for a service that does not need interactive login.

Lock and Unlock a User Account

Lock (adds ! before the password hash in /etc/shadow):

sudo usermod -L username

Unlock:

sudo usermod -U username

Check status:

sudo passwd -S username

L in the output means locked, P means active password.

Set Account Expiration

Set an expiration date:

sudo usermod -e 2025-12-31 username

Remove the expiration:

sudo usermod -e "" username

Change the Comment (GECOS)

The GECOS field typically contains the user's full name:

sudo usermod -c "Ivan Ivanov" username

View the current comment:

grep username /etc/passwd

Verify Changes

After any modifications, confirm the /etc/passwd entry looks correct:

grep username /etc/passwd

Entry format:

username:x:1001:1001:Full Name:/home/username:/bin/bash

Fields in order: login, password (x = stored in shadow), UID, GID, GECOS, home directory, shell.

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