Backup / Restore

shazeal · Posted: Tue Oct 29, 2013 7:35 pm Post subject: Backup / Restore

Hi,

Short Version (TL;DR): Can anyone give me a solid backup / restore system for Gentoo that actually works.

Long Version ...

I have had hardware problems over the last year that required restoring Gentoo from backup. Every time my restore has failed to work.

Before I go onto what happened with the restores. I will list how I backed up the software.

The machine was running stable Gentoo with a custom kernel using a Pappy's seed. All hardware was configured correctly, and everything built-in not as modules.

Firstly I used a stage4 style backup, backing up the "essential" system files everything apart from home and system generated directories.

eccerr0r · Posted: Tue Oct 29, 2013 8:00 pm Post subject:

How far does the kernel get? I'd assume there's a problem with the kernel instead of tar or rsync (unless you have extraneous files lying around when restoring over a broken system versus a wiped disk... this is a different problem).

I personally have been doing system backups this way as well (except I do full system, including /home, /etc, and /var), which has been working mostly (Gnome tends to sometimes break but usually is OK). However I still have to handle the boot loader separately - whenever I do a restore, the boot loader needs to be reinstalled manually. The kernel tends to be in a different partition so that needs to be backed up separately.
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shazeal · Posted: Tue Oct 29, 2013 8:54 pm Post subject:

Each time I have completely repartitioned the disk. The kernel just hangs after grub, then If I re-compile/re-install the kernel+grub via a bootcd/chroot it gets to detecting the "root" disk and fails. It never gets to passing off to Init. I believe the last time I did actually get it working by copying the kernel config from my debian box.
But even redownloading the source and recompiling the old built-in kernel resulted in non booting kernel, which tbh makes no sense. The partition numbers never changed, I wasnt using UUID, and like I said the AHCI controller stuff was built into the kernel.

I guess it could be how I am actually doing the restore / sequence I am doing things. Could you detail the steps you take when restoring?
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shazeal · Posted: Tue Oct 29, 2013 8:55 pm Post subject:

Also which kernel setup do you use?
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CFLAGS="-OmgWTFR1CE --fun-lol-loops --march=asmx86go"

eccerr0r · Posted: Tue Oct 29, 2013 10:17 pm Post subject:

The theory is if you back up your kernel image, it should work as is - and I do save that binary. There should be no reason to recompile.

From what I'm seeing, if you're using grub, you are getting the grub boot menu. You select the kernel, and then the kernel does or does not start running? It seems you're implying it does get to disk detect...

So is it failing with "cannot find root disk" ?

Or is it hanging just before "Starting init"?

Can you set your init to /bin/bash?

One thing that you must get right is your /dev partition. Make sure you have /dev/null, /dev/console, and /dev/zero in your archive correctly. Many things will puke badly without these set, even with udev.

(Come to think of it I'm now pretty certain your /dev is probably what's causing your machine to not boot properly. On a udev system, especially if you copy/tar excluding /dev, it will of course not tar the contents of that directory - and leaving it empty will cause issues.)

shazeal · Posted: Wed Oct 30, 2013 12:22 am Post subject:

That makes perfect sense about the /dev stuff, it is booting upto cannot find root disk and not seeing /dev/sdx. How do I handle this with tar / rsync then? Or would it just be easier to extract /dev from a stage3 tarball?
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CFLAGS="-OmgWTFR1CE --fun-lol-loops --march=asmx86go"

shazeal · Posted: Wed Oct 30, 2013 12:32 am Post subject:

Just to confirm unpacked /dev from a stage 3 and its packed with stuff. No wonder it never worked.

EDIT: Also noticed /run/openrc is a thing! So even if the kernel had recognised the dev stuff openrc would have failed I am guessing?
I think thats what happened with the debian kernel I put in the gentoo partition it got to Init but just bailed.
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CFLAGS="-OmgWTFR1CE --fun-lol-loops --march=asmx86go"

eccerr0r · Posted: Wed Oct 30, 2013 6:11 am Post subject:

Udev/openrc should populate /dev with the correct entries as long as the three base entries are there (console, null, zero). However devtmpfs is needed now in the kernel for udev, but since you had a working machine, it should still work on restore...

I don't know what kernel Debian uses but if it does not have devtmpfs it will not work with Gentoo init.
_________________
Intel Core i7 2700K/Radeon R7 250/24GB DDR3/256GB SSD
What am I supposed watching?