On Mon, Jul 17, 2017 at 08:18:25AM -0400, Nick Holland wrote: > On 07/17/17 05:50, Raimo Niskanen wrote: > > On Fri, Jul 14, 2017 at 10:46:14PM -0400, Nick Holland wrote: > >> On 07/14/17 09:00, Raimo Niskanen wrote: > >> > Hi misc@. > >> > > >> > I wonder how to restore from an /altroot backup? > >> > > >> > (I missed that pax -r happily writes absolute paths and wrote over > >> > /etc from a backup file of another machine) > >> > > >> > > >> > Is it to dd(1) back all but the first 16 blocks - the reverse of what > >> > daily(8) does? Is that all that is needed? > >> > >> don't... > >> > >> > (I missed to skip the first 16 blocks, and I used the block devices > >> > instead > >> > of the character devices. The result was a vegetable, and would like to > >> > understand which of my mistakes that were fatal.) > > probably worth answering why this failed... > 1) The first 16 blocks are where the disklabel is hiding on the first > partition (usually, 'a'). Blindly copy over a disklabel from the wrong > disk, you will blow away your current disklabel. BEST case (both disks > have the exact same layout), you just changed the DDUID of your target > disk. > > 2) writing to sd0a/wd0a instead of rsd0a/rwd0a just drops the data in > the wrong place. This error probably saved your disklabel, so it's a > good error to combine with the first. Didn't help anything, but kept > the damage from being worse.
Strange. It seems I got a wiped disklabel. Anyway not worth digging into anymore. Thank you for the insight! > > >> yeah, that's why. It CAN work, but ... it is the hard way and it's > >> error prone. > >> > >> better way: let's say sd1k is your /altroot... > >> > >> # mount /dev/sd1k /altroot > >> > >> now...it's just a normal file system on a normal place. Copy out > >> whatever you want. umount it when done, please. > >> > >> Nick. > > > > Yes, thank you! That is the safe way. In this case I wanted to get rid > > of all files that my pax fumbling had put there, so I wanted to clear the > > root filesystem and copy back all from /altroot. But then I also would > > have ro run installboot on the restored root filesystem, right? > > > > Is that the right(tm) way to do it? > > If you copy files from any backup back to root, yes, you will need to > re-run installboot. This has to be done any time /boot could have moved > to a new physical spot on the disk. > > If you really want to blow things completely away, give consideration to > doing an "upgrade" (to either what you were running or most recent > release, or even -current), then restoring your /etc/ directory, and > re-running sysmerge afterwards (if you change versions). > > Nick. A maybe some day useful trick indeed. Thank you! -- / Raimo Niskanen, Erlang/OTP, Ericsson AB
