Mac OS X and certain distributions of Linux do not have the root user enabled by default. You can use the “sudo” command to assume root privileges when you need it, but this inconvenient at best. So, enable the root user:
Mac OS X
Open the “Directory Utility” from inside “Utilities”, which is in your “Applications” folder. Click the lock icon in the bottom-left of the window and enter your admin password when prompted.
Enabling the Root Account in Mac OS X's Directory Utility
From the “Edit” menu, select “Enable Root User”. Enter a password for the root account to use, and then click OK. If you need to disable it, repeat the process, selected “Disable Root User” from the “Edit” menu.
Linux
In order to enable the root account in Linux, issue the following command in a terminal window:
sudo passwd root
This will essentially use super-user privileges from sudo to set a new password for the root account. In order to disable the root account again, issue the command:
sudo password -l root
Becoming Root
Now you’ve enabled your root account, whenever you’re in a terminal window, you will be able to issue the command:
su root
This will start a new shell with you logged in as root.