[knc1]

Is this machine the one described in your user information block? (KT-v5.1.0)
I don't own one of those myself, but ...

I often see the use of a non-standard command in the various de-bricking and modification threads.
As if there exists something that takes care of all the details for a user.
You could browse those threads for how to spell and use it. I don't trust my memory enough about it to mis-quote its use here.

But as a general note -
You don't have to umount/mount a file system to change ro/rw or rw/ro
There is an option for that "mount -o remount,rw ..." or "mount -o remount,ro ..."

And a note to all readers:
The man(ual) command is your friend. If you don't have a Linux (or any *nix) system with the documentation installed, google knows it also:
google: man mount

EDIT:
I see that two members beat me to it, giving you the exact, Kindle specific, details.
Too bad we can't delete these posts ourselves... Oh, well...