I have an embedded system that has an (always) read-only root filesystem with a writeable filesystem overlayed on top of it. However, I'm having problems on system shutdown unmounting or remounting it as a read-only filesystem (which results in things like orphan i-nodes and such when it's checked on the next boot).
# mount -o remount,ro /initrd/root-overlay/ mount: mounting /dev/mmcblk0p7 on /initrd/root-overlay failed: Device or resource busy The system boots up with an initrd image that performs the filesystem mounting, before continuing on with the boot. We do this in the initrd's linuxrc file because sometimes we want to select another partition as the root filesystem. Here is the linuxrc script that's setting up the root partition and its overlay: echo "Mounting /proc..." mount -t proc none /proc echo "Mounting /dev/mmcblk0p5 on /ro-root..." mkdir -p /ro-root mount -o ro -t ext4 /dev/mmcblk0p5 /ro-root echo "Mounting /dev/mmcblk0p7 on /root-overlay..." mkdir -p /root-overlay mount -o rw -t ext4 /dev/mmcblk0p7 /root-overlay echo "Creating union of /ro-root and /root-overlay on /realroot..." mkdir -p /real-root mount -t aufs -o br:/root-overlay=rw:/ro-root=ro none /real-root echo "Pivoting to /real-root... initrd will be at /initrd." cd /real-root mkdir -p initrd pivot_root . initrd echo "Unmounting /proc..." umount /initrd/proc echo "Unmounting /dev..." umount /initrd/dev echo "Executing real init..." exec /sbin/init I'm guessing that there might be special syntax that I can use with the mount command (passed via the -o option) to accomplish this, but I don't know what that is. I'm open to alternate ways of performing the initial mounting of the filesystems, if it's necessary. Thanks, Steve
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