How to predict drive number change for 7.3->8.1 upgrade?

Stefan Bethke stb at
Thu Sep 16 09:29:36 UTC 2010

Am 16.09.2010 um 11:05 schrieb Michael Sperber:

> I just upgraded my desktop system from 7.3 to 8.1, and the main hard
> drive, which was /dev/ad6 before is now /dev/ad10.  Consequently, the
> initial boot failed when trying to mount the root file system from ad6.
> The desktop system is now fixed, but I also have a rented server with
> only a serial console, and I worry that the upgrade is going to leave me
> with a dead machine.  Is there any way to predict how the drive number
> changes?  (Why does it change at all?)  If so, what's the proper way to
> tell the system the initial root device *before* rebooting?

If you have a serial console, you can always enter the root device at the prompt, so you can recover there.

If you can figure out the new device name, you can simply change the fstab entry for /; that's where loader picks up the root device that it hands to the kernel.

Long-term, the best option is to label your filesystems or partitions, and use the label entries in fstab instead of the device names.  I don't remember what 7.3 offers in terms of labels, but glabel should be available.  Check tunefs if it offers the -L volname option, that's even better.


Stefan Bethke <stb at>   Fon +49 151 14070811

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