cp /etc/gdm/gdm.schemas /etc/gdm/gdm.schemas.backup

nano /etc/gdm/gdm.schemas

and locate

`<schema>
<key>daemon/AutomaticLoginEnable</key>
<signature>b</signature>
<default>false</default>  Change this to true.
</schema>`

And finally edit this:

`<schema>
<key>daemon/AutomaticLogin</key>
<signature>s</signature>
<default></default>  Put the username here.
</schema>`

If you have look a bit further down, you’ll find options how to enable timed login too, if you use that instead you must leave auto login disabled.

Thanks to this post on linuxquestions that led me to the answer.

Update: edited post with better example.

Update 2!

Thanks to JGV in the comments below for pointing this out!

The even simpler solution:

`* edit /etc/gdm/custom.conf
* add section [daemon] to this file
* inside this section, add lines:
AutomaticLoginEnable=true
AutomaticLogin=username`