No need to reinstall your OS

Published: Thursday, Jul 8, 2021
Last modified: Thursday, Jul 8, 2021 (a1b05c7)

A fantastic “feature” of Linux, BSD, and even Windows 10 is you don’t really need to reinstall to migrate an installation to a new computer. A common misunderstanding is if you get a new PC, you must use the new OS install, or install a new copy of your OS. If you’re intending on replacing an existing PC (and disposing of or re-purposing the old one), there is probably no need to reinstall your OS and deal with user data migration.

On Linux if you rip a SSD out of any x86 box, it will probably boot on any other machine, including virtualization software. One example of this is the laptop I am currently typing away on. It is the third laptop for the same Linux installation. Each time I simply either moved the SSD over or duplicated the SSD onto another SSD. Sometimes I have to modify some configuration, as I use Gentoo on my workstation and laptop and it’s not going to do everything for me automagically (or otherwise surprise me with some unwelcome, opinionated defaults).

My NAS has been migrated between multiple rebuilds with no problem. Even switching between SAS Passthrough cards is not a problem. It runs Alpine… but the distro hardly matters in this discussion. All distros will handle booting on random equipment reasonably well. My Desktop has survived a complete rebuild (new everything) and many partial rebuilds. It’s the same install from years ago.

Sometimes on IRC I hear of people having the same install from ago. I think it might be more common in the Gentoo community, but I don’t see this being a distro specific thing, only that Gentoo is a bit less surprising when things break. Clear error messages and doesn’t hide it behind a bunch of tooling that takes a long time to learn.

ยงExample migration

I recently swapped out my HP Elitebook 820 G4 for a XPS 13. Both devices have NVMe SSDs. I saw four options to perform the installation migration:

  1. Install the old SSD into the new laptop;
  2. Remove the old SSD. Install into a USB SSD enclosure. Then copy its contents over (using ddrescue) to the new SSD (using a LiveCD environment);
  3. Boot the old laptop with a LiveCD, make an image of the SSD onto an external drive, then boot the new laptop with a LiveCD, write the image onto the new SSD from the external drive;
  4. Or Boot both laptops with a LiveCD, network them, then the old SSD data to the new SSD on the other machine using the network.

I opted for option 4.

First step is to boot both laptops with live media. I prefer GRML because it’s pretty simple and no frills, yet it ships with normal desktop stuff such as audio, if you really need it. It has a boot option to load the entire live media into ram, thereby allowing you to remove the bootable media. (One could also PXE boot to achieve similar effect.) I simply booted each laptop from the same usb, using the option to load into memory. Next up was to set up a network. In this case I had 1Gb ethernet interfaces on both devices (the XPS 13 has ethernet via a USB-C dock). I simply ran grml-network on both, said no to DHCP, set each to a RFC 1918 address in the same configured subnet. Ping one host from the other and verify it works. Next is a bit muddy, because it in theory did not work perfectly, but it did achieve the intended results.

I ran nc -l 1234 | pv > /dev/nvme0n1 on the new machine. Then I ran pv /dev/nvme0n1 | nc 192.168.0.1 1234 on the donor machine. It took about 2.5 hours for coping an entire 1TB SSD. In retrospect I believe this could have been faster had I used 10Gb ethernet or a USB enclosure, but it got the job done.

One gotcha is when the imaging finished, nc/pv hung on both sides. I could tell they were finished because no more progress was being made. And they were at the progress of the size of the donor machine’s storage. This is not a good thing to experience, so any recommendations to get better nc ... | pv ... to exit is welcome ๐Ÿ˜.

Next up was booting. I just rebooted and it worked. Note: I set up my grub installs to boot both with MBR BIOS systems and UEFI systems. So tell your friends, you don’t need to pick ‘n choose how to boot your PC, just boot it either way if you set up grub to support both.

ยงMigrating Windows Installs

I don’t know if it is realistically feasible to migrate a pre-Windows 10 install, but with Windows 10, one can simply yank the OS disk and install it in the new PC. If you need to copy tho install onto a soldered SSD, or are upgrading the storage, you can just image the entire original storage device onto the destination storage device. One can use gparted to resize Windows. Surprisingly, Windows will handle this - previously Windows would get upset if the NTFS C: partition is resized without special treatment.

Alternatively, there are vendor tools that can streamline this process, such as Samsung Data Migration tool.1

One gotcha - even if you successfully migrate your Windows 10 install to a new box, you may have to reactivate the license… you’ll find out.

ยงSome other gotchas

If you need to resize an install, it might be feasible without much trouble. If you’re growing a Linux install, usually one can just resize the partitions/block devices in gparted/parted, then run grow2fs(8) on the filesystems. If you’re using LUKS encryption it appears to take its size from the size of the block device it resides on. AS for LVM2, see pvresize(8).

Shrinking is a bit trickier because you will have to adjust the LVM2/LUKS/filesystems before shrinking the partition itself. Shrinking can be trickier because doing partition table math is hard. You’ll have to carefully ensure you shrink the filesystem, then shrink the block devices, and partitions in order. I haven’t quite figured it out but it feels like guesswork to get the sizes just right, so it might be easiest to shrink the filesystem, LVM2 physical volume, LUSK, etc to be extra small, but a bit bigger than whatever they contain. Then just “grow” each filesystem/block device after the partition is finally shrank. This way you don’t need to do exact math. Recap: Shrink everything be too small starting with the filesystem working your way out, then grow everything inside the partition with growing the filesystem last.

Backups! Backups! Backups! If you are doing anything with data, it doesn’t exist if you don’t have backups that you can restore from. Ideally you want at least two copies. When imaging anything, it’s usually a good idea to keep a copy of the original image until you’re satisfied with your handywork. Better safe than sorry. Data storage is cheap… or if you afford backups for your storage, you can’t afford your storage (as it doesn’t exist without backups).

ยงConclusion

I think my details were a bit streamlined, but I wanted to keep this short. If the reader takes anything away from this post, most modern OS installs are portable between hardware, and are easy to install onto new storage. Reinstalls shouldn’t be a thing of necessity, but an action of policy only - if you are re-purposing a machine, by all means reinstall, but no need to do it when migrating.

As always I should shout out a live media to use for this post — GRML linux is great for this.


  1. Thanks smokey991 for suggesting this. ↩︎

<< Previous post
Next post >>