Remount rootfs read-only

Question

I am having a very strange error on an embedded ARM board (poky, kernel 2.6.35). I try to remount / read-only because the device sometimes reboots (hardware watchdog) and I want to avoid file system inconsistencies. I did this in the past with another board without problems, but on this particular system doing a "mount -o remount,ro /" results in a "mount: you must specify the filesystem type" which is not an error I would expect, ever.

"mount" is from util-linux-ng 2.17.2 and I also tried util-linux 2.19.1. The root file system was formatted with "mkfs.ext4 /dev/sdg2 -L rootfs -O extent,^large_file". /etc/mtab is linked to /proc/mtab.

Any ideas?

Answer 1

This error message is misleading. Try specifying the full mount command, i.e.

mount -o remount,ro -t $FSTYE $DEVICE /

and you should most likely get "mount: / is busy". Compare http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=154978