Thanks for your quick reply. In fact, I've remounted root as rw.
I've seen three kinds of instructions:
1. mount -o remount and rw /
-> Error "mounting and on /rw failed: No such file or directory
2. mount -o remount,rw /dev/root
-> Error "can't find /dev/root in /etc/fstab
3. mount -o remount,rw /
This one succeeded, but I was greeted with the above problem.
Oh, I forgot to say that internal MD of my second-handed c3k had been replaced
by a 2GB Sandisk Ultra II CF card. Don't know if that matters.