root partition will not remount
 

I'm running centos6 64bit and I've got my root partition in read-only mode. I need to do some zero'ing and that will only work with the parition in ro. I'm trying to change it to back to rw but it always throws this error:
the command I used to change it to ro was: and it worked fine, I'm now trying to switch it back to rw with this command:
but it won't work, I just get 'mount: / not mounted already, or bad option' all the time and it's driving me batty. Can anyone help?

You might have to unmount it to remount.

thanks but that didn't work. I did: and the cursor dropped to the next line and then I did and I got:

What does fstab say?

With the root filesystem mounted read-only, the failure might be the mount command's inability to update /etc/mtab. Try adding the "-n" (--no-mtab) option to block the mtab update. If that works, you can run it again with "-f" (--fake) in place of the "-n" to just update /etc/mtab.

thanks for the responses here. I've found 'a' solution which is a reboot of the machine. If I reboot and then run as a first action it works and I can change the root partition to rw.