GEOM Boot Problems, fixing

gmirror boot problems

How to fix boot problems caused by errors in loader.conf when using GEOM/GMIRROR

Recently I had a problem where adding an entry into loader.conf caused my machine to fail at boot stage 3 (/boot/loader). This problem was compounded by the fact my boot disks were running on a GEOM mirror; the GEOM module not being loaded by a FixIt cd and my inability to load it using kldload once FixIt was loaded.

Background I have scsi 4 disks on dual bus. Disks 1 and 3 are a gmirror (/dev/mirror/FreeBSD) and hold my whole FreeBSD install. The other 2 are for data and are using setup using a zfs stripe (but not relevant). After making an addition to /boot/loader.conf and rebooting, the bootstrap hangs at /boot/defaults/loader.conf. So, I presumed the entry I just made was causing problems.

Normally, booting to a FixIt CD, mounting /boot and editing the file would have resolved this sort of problem. However, the geom_mirror module isn't loaded into the kernel by the disc and as such, there is no /dev/mirror/FreeBSDxxx to mount. I was also unable to add the module manually because either kldload was unavailable; or it returned an error (I forget which now).

To get around this problem I performed the following steps:

1) break out to the loader prompt during boot from CD