The root user always has a user ID of 0, and is the only user that can do anything on the system, like modifying permissions on any file including the root directory.
Switching to Root
To switch your user account to use root, you can use the su command and enter the password. You can also use the sudo command to run another utility or command as if you were the root user, which is the most common method on a Debian-based operating system like Ubuntu.
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