How do I reset/recover my superuser password without the boot disk?

I lost the superuser password for my iMac and I don't have the boot disk. I already tried the second answer on this page, but every time I type su from the command prompt, it still asks for a password that I don't have anymore. Is there another way to reset the superuser password?

sudo passwd root

Enter YOUR password and you're in.

If you have an administrator user account set up on your Mac in addition to the root account, you can use the Directory Utility to do the following:

1. Open the Directory Utility from /System/Library/CoreServices or in OS X 10.11 and later, System/Library/CoreServices/Applications.

2. Click the lock button and authenticate as an administrator:

3. Go to the menu Edit > Change root password...:

4. It should prompt you to enter a new root password:

Again, you have to have access to an administrator account to do this (so you can authenticate).

Good luck.

The best solution for 10.7 and 10.8 is to boot in recovery mode (CMD+R). Then, open a terminal window and type the command "resetpassword". This will open a window which will allow you to reset any user's password.

http://osxdaily.com/2011/08/24/reset-mac-os-x-10-7-lion-password/