Unmounting root filesystem without rebooting the server

Solution 1:

How about using pivot_root to switch to a temporary, in-memory filesystem root?

See http://www.ivarch.com/blogs/oss/2007/01/resize-a-live-root-fs-a-howto.shtml.

Solution 2:

You could use dd and netcat to copy the disk/partition somewhere else and do the recovery there.

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Solution 3:

I would try to get someone to help you with a live rescue CD like the PLD Linux Rescue disk. But only having ssh access, no KVM, no ILO, no backups, etc. is pretty risky.

One other option is to install the free Hot Copy snapshotting utility from R1Soft(hcp): See: http://www.r1soft.com/tools/linux-hot-copy/

It would allow you to take a read-only snapshot of your root partition and mount it to a subdirectory. You could run your undelete/repair utility against the snapshot mount.