There described different common Apple keyboard shortcuts,
Startup keyboard shortcuts, etc.
Resetting a root or account password
The most common way described in the internet and on the Apple site too is
to boot from Apple Mac OS X Installation Disk, which come with new Mac OS computer,
(http://support.apple.com/kb/HT1274 - Mac OS X: Changing or resetting an account password )
and to change the admin password via graphical tool.
But what I should to do, if I have for example a MacBook without an Installation Disk?
Apple suggest to bye an Installation Disk, but there is a really easy way to reset the admin password.
I really don't know why Apple don't share this method.
It's very very easy.
You just need to boot into single user mode and change the password from shell prompt.
For booting into single user mode press "Command-S" during Mac OS startup.
Next you will be prompted into root shell #
Then you should remount a root partition into Write mode.
# /sbin/mount -uw /
Next, you may change the password for root or any other account by simple command: