The Ultimate Guide to Migrating a User on Linux: Ownership, Groups, Crontab, Config Files, and More

I recently had a request to replace a user on the Linux server. This Linux user has a lot of files, folders and cronjobs that I need to move to the new user. This may sound like a simple task, but it's not. In this article I will show you the steps to make this change successful.

Let's get started!

Notes:
Old user: OLDUSER
New user: NEWUSER

Replace the name before executing these commands!

1. Before starting the process, make sure that the new user (NEWUSER) already exists on the system:
   id NEWUSER
   
   
2. Log in as a root user.
   sudo su
   
   
3. Move files from the OLDUSER user to NEWUSER, if there are any:
   mv /home/OLDUSER/* /home/NEWUSER/
   
   Note: Changing file and folder permissions later 
   
   
4. Check which groups the OLDUSER user belongs to:
   groups OLDUSER
   
   If there are any (except those named OLDUSER), add the NEWUSER user to it/them:
   sudo usermod -a -G groupName NEWUSER
   
   
5. Change the ownership of files and folders on the whole system from OLDUSER to NEWUSER:
   find / -user OLDUSER 2>/dev/null -exec chown NEWUSER {} \;
find / -group OLDUSER 2>/dev/null -exec chown :NEWUSER {} \;
   
   Note: These commands search for all files and folders owned by OLDUSER, and then change the ownership to NEWUSER one by one.
   
   
6. Check which process is running by OLDUSER user:
   ps -ef | grep OLDUSER
   
   
7. Also check the systemd service files:
   grep -rli "OLDUSER" /etc/systemd /usr/local/lib /usr/lib/systemd 2>/dev/null
   
   After modifying at least one service file, reload the systemd daemon:
   systemctl daemon-reload
   
   
8. Make sure the old user doesn't have any crontab entries. If there are, migrate them too.
   
   Check and print it out:
   crontab -l -u OLDUSER
   
   You can edit the crontab of NEWUSER with this command:
   crontab -e -u NEWUSER
   
   Or simply migrate the crontab with this command:
   mv /var/spool/cron/olduser /var/spool/cron/newuser
service crond restart 
   
   
9. Then check all crontab entries for the OLDUSER user by running the following command:
   grep -rli "OLDUSER" /etc/cron* 2>/dev/null
   
   
10. Also check the OLDUSER user in the /etc directory:
    grep -rli "OLDUSER" /etc 2>/dev/null
    
    If there is a configuration file here that contains OLDUSER, replace it with NEWUSER one at a time.
    
    
11. Reboot and see if everything that worked under OLDUSER works.

That's all.

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