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SCAN_FFS(8) System Manager's Manual SCAN_FFS(8)

scan_ffsfind UFS/FFS partitions on a disk

scan_ffs [-lsv] [-b begin] [-e end] device

This is the life-saver of typos. If you have ever been working too long, and just happened to type 'disklabel -w sd0 floppy', instead of 'disklabel -w fd0 floppy', you know what I am talking about.

This little program will take a raw disk device (which you might have to create) that covers the whole disk, and finds all probable UFS/FFS partitions on the disk. It has various options to make it go faster, and to print out information to help in the reconstruction of the disklabel.

scan_ffs works only on FFS file systems, not FFS2 file systems.

The options are as follows:

Tell scan_ffs where to begin searching for filesystems. This makes it easier to skip swap partitions, or other large non-UFS/FFS partitions.
Ditto for telling scan_ffs where to stop.
This will make scan_ffs print out a string looking much like the input to disklabel. With a little massaging, this output can usually be used in the disklabel edit.
This tells scan_ffs to be smart about skipping partitions (when it thinks it found a valid one). By not scanning partitions for superblocks, the program completes a couple of orders of magnitude faster. However, sometimes being smart is too good for its own good, especially if your disk has had a different layout previously, or contains other non-UFS/FFS filesystems.
Tell scan_ffs to be verbose about what it is doing, and what it has found.
This specifies which device scan_ffs should use to scan for filesystems. Usually this device should cover the whole disk in question.

The basic operation of this program is as follows:

  1. Panic. You usually do so anyways, so you might as well get it over with. Just don't do anything stupid. Panic away from your machine. Then relax, and see if the steps below won't help you out.
  2. Try to find your old disklabel by any other means possible. This includes printouts, backups (look in /var/backups/), screendumps, and whatever other method you can think of. The more information you have, the better your chances are in recovering the disklabel of the disk.
  3. Create a disklabel on the affected disk, which covers the whole disk, and has at least one partition which covers the whole disk. As the “c” partition usually covers the whole disk anyways, this sounds like a good place to start.
  4. Run scan_ffs over this partition. If you have any information about the disklabel which used to exist on the disk, keep that in mind while scan_ffs spews out its things.
  5. Use disklabel(8) to reconstruct the disklabel on the affected disk, using all the information you gathered from scan_ffs and other sources.

Last but certainly not least, we wish you good luck. The UFS/FFS filesystems are pretty sturdy. I've seen them reconstructed after some pretty weird and awesome fumbles. If you can't have backups, at least have funky tools to help you out of a jam when they happen.


February 10, 2019 OpenBSD-7.3