Category: Linux

I was working with a C.H.I.P and the SSH host keys were regenerating each boot after upgrading to Stretch. This caused a host key mismatch every time. It turns out /etc/rc.local was a script which checked for the presence of SSH host keys, including DSA, and if found all of them it replaced itself with /etc/rc.local.orig, which is the stock does-nothing script. If it didn’t find all of them, it would delete any existing keys and regenerate all of them.

I still don’t understand why this produced the behavior it did, because the script did succeed in producing DSA keys, but replacing the weird /etc/rc.local with the /etc/rc.local.orig that just exit 0s seems to have solved the problem.

Not having snapshots on ext4 finally got too annoying. I was able to copy the root filesystem off, then format with btrfs and copy it back on. I used System Rescue CD to do this, turn off Copy on Write on database files, and edit /etc/fstab with the new filesystem and UUIDs. It worked! Eventually. There were a few snags:

• Grub gets angry when you wipe all your partitions. I’m still not clear on what the UUID it was looking for was, because it didn’t look like the old root filesystem. Using System Rescue CD’s Super Grub Disc image I was able to boot into the system and run update-grub and install-grub, which fixed it.
• tar with bzip2 is slow. Using tar without compression ended up being much, much faster.
• Taking out the drive with the swap partition caused the boot to hang until timeout. There isn’t an mkfs.swap, but there is a mkswap.
• The script I used to disable CoW didn’t preserve ownership information, so I had to re-chown things appropriately. Oddly PostgreSQL still started, but MySQL did not. That was nice because it alerted me to the problem.

Hooray for snapshots! I’m hoping to set up snapshot backups Soon. (TM)

I removed my dad’s Linux installation; it was more than two years old and he wasn’t using it, so it just took up half his hard drive as that’s how we had partitioned it. Getting rid of GRUB was the first step, so I booted into the XP recovery console from the installation disc. I was prompted for an Administrator password, but it turned out to be blank, so I just hit enter. Woo, security. I didn’t run bootcfg /rescan or fixboot; fixmbr alone was enough to do it. It successfully booted with the Windows bootloader upon restarting, so I used the XP partition manager to remove the Linux partitions. I couldn’t seem to remove the extended partition, nor resize the volume, which made sense because the extended partition was there.  I booted up into System Rescue CD, fdisk’d away the extended partition, then fell back to GParted to expand the single remaining partiton and its filesystem to fill the drive. Presto: double the free space available to Windows!

I also decided to try to dual-boot Debian Squeeze and Debian Wheezy on my netbook. This is because in Physics 260 we use python-visual in our computer homework, and the version in Squeeze has a problem that results in simple renderings containing, for instance, nothing but a sphere and a box taking seconds per frame. The error message i915_program_error: Exceeded max instructions is also emitted. I used the Debian installer’s guided full-disk encryption to set up this machine, so I have an ext2 partition mounted as /boot, then logical volumes for /home, /, and swap within an encrypted LVM. I wasn’t sure if two installations of Debian sharing a /boot partition was a good idea, but I assumed it wasn’t and so halved the existing one and added another ext2 partition for the new installation. I wonder if ext3 is a more dependable choice. Then I had to make another logical volume in the encrypted volume group for use as / for the Debian Wheezy installation. After poking around online to get an idea of what to do, I booted into a LiveUSB, started with cryptsetup luksOpen to open the encrypted container. Then vgscan to find volume groups, and vgchange -a y to make the logical volumes available. LVM is an alternative to partitions, so I then shrank my /home with resize2fs, then shrank the logical volume around it with lvreduce. It was a little scary when resize2fs and lvreduce appeared to treat units differently, but it seems to have been fine. If my understanding is correct, resize2fs reports size in 4kiB blocks (which it prints as 4k), and lvreduce speaks of base 10 units, yet seems to mean base 2. lvcreate was the easy part.

Amazingly, my system still booted after all this, so I installed Debian Wheezy. It took some fiddling to get partman to recognize the contents of my logical volumes. I had to trigger loading cryptsetup by going into the encryption setup, (IIRC pressing finish, same for LVM) then used cryptsetup, vgscan, and vgchange as before, then going out of and back into partman. The bootloader failed to install, but I continued without it and ran update-grub once back in Squeeze and although it detected Wheezy in the LVM, the entry it generated wouldn’t boot because it fails to prompt for the crypt container’s passphrase. I’m not sure why; that’s about as far as I’ve gotten. I tried without a separate boot partition and as would be expected it couldn’t even find the kernel. There are wishlist bugs filed in Debian about the installer’s support for encrypted LVM: #498199, #529343, and #566497 to name a few. I hope I can figure this out, but I don’t feel comfortable spending a great deal of time on it. I may just install to my flash drive.

Edit Jan 11, 2012:
I got it working! It wasn’t prompting for the passphrase because it was missing /etc/crypttab. Once I added that and chrooted in from the installer’s rescue mode to generate a new initramfs with update-initramfs -u, it worked! Hooray!