After the launch of the highly successful Motorola Droid, Motorola started shipping its phones with locked down bootloader. These highly locked down bootloader severely restricted the modding capabilities of Moto phones.
One of the most talked about phones this year the Motorola Atrix 4G also ships with a highly locked down bootloader. However, the highly talented developers at XDA managed to get root access to the phone system’s partition in quick time.
In fact, at the moment many Custom ROMs are also out for the Atrix (They are not AOSP based, though).
Now, another awesome developer Sogarth has got a full-blown Linux distro, Ubuntu, up and running on the Atrix 4G. This mod is obviously not meant for the faint hearted, and newbie Atrix owners are highly recommended to stay away.
Possibilities of bricking your beloved Atrix or putting it into an infinite reboot loop are also very much possible. As usual with these mods, a few caveats do exist like installing certain packages can break the Ubuntu installation etc.
The highly complicated steps of installing Ubuntu on the Motorola Atrix 4G can be found here.