How to change a username in Linux.

Changing a username in Linux is straightforward but requires careful steps to ensure all related system files and processes are updated correctly. This post will walk you through the process to ensure everything functions smoothly after the change.

Steps to Update a Username

1. Log in as Root (not Recommended) or Use sudo (Recommended)

Before making any changes, ensure you have administrative privileges. You can either log in as the root user or use sudo in your commands (recommended).

2. Check User ID (UID) and Group ID (GID)

It's good practice to check the current user's details before making any changes. This can be done using the following command:

$ id SNUB

Output

uid=1004(SNUB) gid=2001(SNUB) groups=2001(SNUB),27(sudo)

This will display information like user ID (User ID) and group ID (Group ID), which can be useful for preventing potential conflicts with system permissions and file ownership. Again, replace the intended username accordingly.

3. Change Current Username

The usermod command is used to modify user information in Linux.
To change the username, use the following syntax:
sudo usermod -l new_username current_username

Let's apply our change.

$ sudo usermod -l SNUBmonkey SNUB

-l option specifies the new username.
Replace SNUBmonkey with your chosen new name, and SNUB with the existing username.

4. Rename the User's Home Directory (Optional but Recommended)

To maintain consistency, you should also rename the user's home directory:

$ sudo usermod -l SNUBmonkey -d /home/SNUbmonkey -m SNUB

The -d option specifies the new home directory, while -m moves the content from the old directory to the new one.
Replace any references to the old username with the new one.

5. Change Primary Group

When changing a username, changing the primary group to match the new username is good practice for consistency. Keeping the username and primary group aligned simplifies user and group management, prevents confusion in file ownership, and maintains system cleanliness by avoiding old group names lingering in the system.

$ sudo groupmod -n SNUBmonkey SNUB

6. Verify Changes After the Update

After changing a username, it's essential to verify that all updates were successful. A key step is using the id command to confirm the user's new details.

$ id SNUBmonkey

Output

uid=1004(SNUBmonkey) gid=2001(SNUBmonkey) groups=2001(SNUBmonkey),27(sudo)

The output should show the new username along with the original UID and updated primary GID.

7. Check and Update Permissions (If Necessary)

After renaming the home directory, update file ownership across the system to reflect both the new username and primary group.

$ sudo chown -R SNUBmonkey:SNUBmonkey /home/SNUBmonkey/

This ensures that all files in the user's home directory belong to the new user.

8. Update Crontab Entries (If Needed)

After changing a username, you may need to update crontab entries to ensure that scheduled tasks continue to run under the new username. 

List the current (previous username) cron jobs:

$ sudo crontab -u SNUB -l

Then, set the same crontab under the new username:

$ sudo crontab -u SNUBmonkey -e

This ensures that scheduled tasks continue to function correctly without interruption.

9. Reboot (Optional)

Although not always necessary, rebooting the system can help ensure that all processes and services recognize the changes:

$ sudo reboot

And voila!
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