mac – Ubuntu on Powerbook G4 returns to OSX

I installed ubuntu on my old Powerbook G4, however, several things do not work very well (ie, sound, keyboard light, etc.) Therefore, I would like to go back to OSX (I think Mountain Lion or Leopard).

As the computer now runs on Ubuntu, none of the original keystrokes work, for example, command + change + R will connect to an online recovery server.

I completely cleaned the unit when I installed Ubuntu (on my old Windows machine it worked so well that I never used Windows again), so there is no original recovery partition left.

Is there a command line in the terminal that will connect to an OS X recovery server? What other options can you think? The original disc is lost a long time ago.

Thank you,
Kai