Resetting the MacOS X Tiger administrator password can be done by booting with the Installation Disk, and selecting the appropriate menu option. This is the most commonly referred to option, with a lot of high-quality instructions available via Google.
The problem is what to do when you have no disk – or it is too inconvenient to get it. In my case, the PowerPC Mac Mini that runs MacOS X Tiger has a bad DVD drive.
In most cases, resetting a password just requires physical access to the machine and a reboot. (This is why nearly all security professionals say, If you’ve physical access to the box, it’s over.)
With Tiger, you can indeed do this. (In fact, Leopard and Snow Leopard can too – it’s just more complicated.)
Start your MacOS X 10.4 system, and at the gray screen hit (and hold) Cmd-S to enter single user mode. The screen should go black, and white writing commences – kernel messages. You should eventually get a root prompt:
At this prompt, type in these three commands (terminated with a return, of course):
(Replace admin with your administrator user’s short username.) When I did this, I found that if you waited too long after doing the command
sh /etc/rc, then the system would take away your prompt. So don’t lag!
This article (from 2009) over at MacYourself is one of the most complete descriptions I’ve seen; this 2007 article at MacOSX Tips is nearly as complete and adds some more thoughts too.
These articles saved me; I hope they can be of some use to you too.