h3x.no » kvm

Expanding a kVM disk image

Tor Henning Ueland — Sun, 14 Aug 2011 19:24:31 +0000

Had to expand a KVM virtual machine today. Luckily, that`s pretty straight forward. You simply create a new disk image with the extra size needed, merge it into the original disk and voila. Then you just need to partition in the extra space and you are good to go.

How-to:

1: Halt your virtual machine.

You need to stop your virtual machine before going wild with the drive. Virsh stop , or virsh destroy if it somehow wont stop.

2: Create a disk with the extra space needed:

qemu-img create -f raw 5gig.img 5G

3: Merge it into the disk you are working with

cat 5gig.img >> yourdisk.img

4: Boot up and and partition your drive.

Then start up your virtual machine again with virsh start . If you use Windows server, all you need to do is to visit disk managent, right click your drive with little free space and choose “extend partition”. The job takes seconds and does not require any reboot.

Mount KVM/Xen disk image / loop device

Tor Henning Ueland — Thu, 11 Nov 2010 07:45:06 +0000

Working with virtual disks is pretty straight forward. If you have a single partition virtual disk you can mount or fsck the image file directly. It is a bit more work if you have multiple partitions on the disk, but not to worry

First, map op the partitions on the device:

[root@hostname images]# kpartx -v -a imagename.img
add map loop0p1 : 0 8369802 linear /dev/loop0 63
add map loop0p2 : 0 224910 linear /dev/loop0 8369865

This creates mappings for the device that can be accessed easily with for example fsck:

[root@hostname /]# fsck.ext3 /dev/mapper/loop0p1

e2fsck 1.39 (29-May-2006)

/: clean, 87953/1046528 files, 588235/1046225 blocks

You can even easily mount the partitions:

[root@hostname /]# mount -o ro /dev/mapper/loop0p1 /mnt

To clean up after your self (after unmounting any mounted partitions):

[root@hostname /]# kpartx -d /dev/loop0

SysRq-reboot macro for Blackbox KVM software

Tor Henning Ueland — Sun, 15 Mar 2009 18:50:15 +0000

A nice way of rebooting a frozen Linux-based server when you do not have a power switch available is to use the SysRq-abilities. (Ubuntu Example.) Blackbox does not have a default macro installed for just that, but you can create a new macro and insert the following:

“RSEIUB”

This will create a working macro for writing any data in cache to disk, kill all processes (Sigkill), remount mounted disks and perform a reboot.