Build a guest library

I have this exported over NFS to all my local machines:

$ ls -lh /mnt/media/guest-library/
total 12G
-rw-r--r--. 1 rjones rjones 971M Apr 16 23:38 debian5x64.img.xz
-rw-r--r--. 1 rjones rjones 250M Jul 26 23:09 f16x32.img.xz
-rw-r--r--. 1 rjones rjones 809M Jul 26 20:29 f17x64.img.xz
-rw-r--r--. 1 rjones rjones  59M Jul  6 22:19 freedos11.img.xz
-rw-r--r--. 1 rjones rjones 379M Jul  7 20:11 opensuse1113x64.img.xz
-rw-r--r--. 1 rjones rjones 349M Jul  6 22:31 plan9.img.xz
-rw-rw-r--. 1 rjones rjones  126 Apr 16 17:22 README
-rw-r--r--. 1 rjones rjones 384M Apr 18 00:19 rhel3x64.img.xz
-rw-r--r--. 1 rjones rjones 471M Apr 18 00:15 rhel4x64.img.xz
-rw-r--r--. 1 rjones rjones 848M Apr 16 17:02 rhel5epelx64.img.xz
-rw-r--r--. 1 rjones rjones 768M Jul  7 07:21 sl60x64.img.xz
-rw-r--r--. 1 rjones rjones 148M May 23 16:08 ubuntu1204ppc.img.xz
-rw-r--r--. 1 rjones rjones 1.1G Apr 16 17:09 win2003.img.xz
-rw-r--r--. 1 rjones rjones 3.4G Jun  1 10:46 win8-preview.img.xz
-rw-r--r--. 1 rjones rjones 2.1G Apr 16 20:28 winxp.img.xz

Having a library of images which are (relatively) small like this is great for testing. If someone gives me a bug and it happens to affect one of the guests I have saved, then I can just unpack that guest, virt-resize it to the right size and off I go, and that’s usually a lot quicker than installing a new guest, particularly when you’ve got only slow ADSL.

Adding a new guest is easy using virt-sparsify and xz. Note I’ve set the temporary directory (TMPDIR) to somewhere with plenty of space.

$ sudo TMPDIR=$(pwd) virt-sparsify /dev/vg_pin/F18Rawhidex32 f18rawhidex32.img
Create overlay file to protect source disk ...
Examine source disk ...
 100% ⟦▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓⟧ 00:00
Fill free space in /dev/vda1 with zero ...
 100% ⟦▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓⟧ --:--
Fill free space in /dev/vg_f18rawhidex32/lv_root with zero ...
 100% ⟦▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓⟧ --:--
Clearing Linux swap on /dev/vg_f18rawhidex32/lv_swap ...
 100% ⟦▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓⟧ 00:00
Copy to destination and make sparse ...

Sparsify operation completed with no errors.  Before deleting the old 
disk, carefully check that the target disk boots and works correctly.

$ ll -h f18rawhidex32.img
-rw-r--r--. 1 root root 10G Jul 27 14:42 f18rawhidex32.img
$ du -sh f18rawhidex32.img
3.0G	f18rawhidex32.img
$ xz -T 0 --best f18rawhidex32.img
$ ll -h f18rawhidex32.img.xz
-rw-r--r--. 1 rjones rjones 667M Jul 27 14:42 f18rawhidex32.img.xz


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2 responses to “Build a guest library

  1. Darksecond

    How would you integrate virt-sysprep into this workflow?

    • rich

      Darksecond, that’s a good question.

      Either you could create an overlay / snapshot on top of the original guest:

      qemu-img create -f qcow2 \
        -o backing_file=/dev/vg_pin/F18Rawhidex32 \

      and then run virt-sysprep on the overlay:

      virt-sysprep -a overlay.qcow

      before continuing to sparsify the overlay:

      virt-sparsify overlay.qcow f18rawhidex32.img

      Or you could sysprep the guests just before you create/use them. Copy and uncompress the .xz file and run virt-sysprep on that. The advantage of this second method is that you get to choose which virt-sysprep options you want to use.

      For more information see

      The other thing I forgot to mention is that you might want to use virt-resize to choose the final size for the guest.

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