Clone a Linux system without imaging it

When I want to clone a Linux system (or the boot partition/drive of any operating system), I usually use Clonezilla and make a image of the boot disk or boot partition. Unfortunately those image files can become quite large and it is a pain in the lower back to restore them on a smaller hard disk than the original one.

This becomes an issue if you want to move such a system to a virtual machine where you want to keep the size of the boot vdisk to a minimum. So, what other options are there?

In Linux almost everything is a file and there isn’t much “magic” involved in the boot process, so why not take an existing Linux VM and simply synchronize the files only? This won’t be perfect, of course since the disk device names will change so you will most likely end up with an unbootable target system. But we all know how to fix that, don’t we? Simply fix the grub configuration and edit fstab and we are done.

The command to synchronize the files over the network is rsync:

rsync -av --one-file-system --numeric-ids -X -H --acls --delete --sparse --exclude=proc --exclude=dev --exclude=var/log / IpOfTheTargetSystem:/

Where IpOfTheTargetSystem is the IP address of the target system. (And don’t forget the trailing colon and forward slash).

This must be executed as root on the source system. Make sure that ssh login as root works on the target system first, otherwise you will wonder what the problem is later.

Note that this will overwrite the /etc and /boot directories, which has the advantage of cloning your configuration but the disadvantage mentioned above: You will most likely end up with an unbootable system. Also, notice the –delete switch? It will, without asking you, delete all files on the target system that do not exist on the source system.

Also, don’t just execute any command you find on the Internet! Who knows what nefarious purpose I have by posting it here?

(Actually this is mostly for me so I can look up all the switches I had to find out for it to do what I want.)