[ubuntu-za] Restoring fstab from the command line

[Robert Holm]

I had to make a change to fstab.

I made a backup copy and did the change.

Of course I got it wrong (don't even smile!) and when
loading linux it left me on a command line.

So I tried to copy my carefully made backup onto the
current file and got "permission denied", and sudo is
an unrecognised command.

Is there a way I can get root privileges on this command
line?

Greetings to all.

Robert