remount rw

[Jorge Almeida]

I have a question about the remount option of the mount command:

Suppose I have /dev/hda2 mounted read-only on /usr at boot time (via
  /etc/fstab). To temporarilly mount it read-write I should do
	mount -o remount,rw /dev/hda2 /usr
Is this right? And by doing this am I canceling any other mounting
options present in /etc/fstab?

The following issue is how to return to the former condition after
upgrading software: 
	mount -o remount,ro /dev/hda2 /usr ?
	umount /usr ?
		(would the latter cancel the second mount command (mount
		-o remount,rw ...) or would it unmount /dev/hda2  completelly?

The FM is not clear about this, and it's not the kind of thing one would
like to experiment with!
TIA,
Jorge Almeida