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When a (Archlinux) system that has its root on RAID and LVM is misconfigured and does not boot, what steps are needed to recover it?

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Anyone can make a mistake but to make the same mistake three times takes an incredible amount of carelessness. – John Gardeniers Nov 13 '12 at 4:47
@JohnGardeniers ...or a lot of hard work and careful planning. The real trick is making it look like a different mistake, and someone else's fault so you can bill for all the extra hours, though. – HopelessN00b Nov 13 '12 at 15:54
@JohnGardeniers my apologies, I had misunderstood that this site is for people running servers, while it is for people running sites in a /professional/ setting. I am very careless with this server, and I should've posted my question on Linux&Unix instead of here :) Not sure why it's not a real question though. I still think it is useful information, even if it happens just once instead of three times. – Tinco Nov 14 '12 at 21:35
@Tinco, I suggest investing in a UPS to help eliminate this kind of problem. – John Gardeniers Nov 15 '12 at 0:09

closed as not a real question by womble, John Gardeniers, MadHatter, HopelessN00b, mdpc Nov 13 '12 at 17:56

It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot be reasonably answered in its current form. For help clarifying this question so that it can be reopened, see the FAQ.

1 Answer

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First, get a linux live usb stick, I use the debian one and boot from it.

If your server is under a staircase or some other hard to sit location do the following three steps:

1 Become root, type adduser myname and enter your login information.

2 Add the line myname ALL=(ALL) ALL to /etc/sudoers.

3 Type sshd to start the sshd daemon if it is not already running (it is on the debian stick).

Now I assume you are logged into your machine. Type sudo -s to become root.

To find your raid arrays and mount them perform the following two steps:

1 Type mdadm --examine --scan > /etc/mdadm/mdadm.conf to setup the configuration.

2 Type madam --assemble --scan to ready the devices.

Now to mount your LVM partitions do the following steps:

1 Type lvscan to find all your volumes.

2 Type vgchange -ay dirname where dirname is the directory of your volume groups. (for me /dev/data and /dev/array because lvscan shows /dev/data/home and /dev/array/root)

3 For each volume you can now make a directory in /mnt and mount the partition there by typing mount /dev/array/root /mnt/root when root is the name of the partition you want to mount and /dev/array/root the volume it is in.

Now type mkdir /mnt/boot and mount your boot partition there if you have your boot directory on a separate partition I have mine on a raid device too so I type mount /dev/md1 /mnt/root/boot.

Now we have all filesystems setup, it's time to chroot into our broken system. First change into your root directory like so cd /mnt/root. Then perform the following series of commands:

mount -t proc proc proc/
mount -t sysfs sys sys/
mount -o bind /dev dev/
mount -t devpts pts dev/pts/

Now it's time for the main event, type chroot . /bin/bash and you are back into your old system. You can repair it like normal, perhaps run pacman -Syu to install all updates, and don't forget to run mkinitcpio if your kernel changes!

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