Accidentally created user with duplicate UID. How to fix?
On Mac OS X, you can change a UID of a local user using System Preferences > Users &amp; Groups.

Open the padlock there to allow changes to be made and then right-click on the user you like to change.

NOTE: You should not be logged in to that account at the time you do the change.

Also, POSIX permissions will follow the UID, so after changing it you may need to change the user ownership for that home folder or you would face not to be able to log in to the changed account.

Command for changing ownership would be:

sudo chown -R &lt;account_name&gt; /path/to/userhomefolder