If you run KVM with enabled monitor management console, you can do some pretty powerful internal stuff while the KVM guest is running.

In order to have a KVM-Qemu management console, you should start KVM with something like:

-monitor telnet:127.0.0.1:3010,server,nowait,ipv4

See the official documentation of Qemu for more details and also the man page of qemu-kvm (unofficial mirror).

Once you have it set up, you can then telnet to the management console and review the available commands:

famzah@famzahpc:~$ telnet localhost 3010
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.

QEMU 0.11.0 monitor - type 'help' for more information
(qemu) help

Changing the ISO image of a virtual CDROM drive is quite easy:

• First review what the current status of the drives is:

  (qemu) info block
  virtio0: type=hd removable=0 file=/dev/sdb-vol/win7 ro=0 drv=host_device encrypted=0
  ide0-cd0: type=cdrom removable=1 locked=0 file=/shared/win7-eval.iso ro=0 drv=raw encrypted=0
  ide1-cd0: type=cdrom removable=1 locked=0 [not inserted]
  

• Then change the mounted ISO image in the CDROM drive on the fly:

  (qemu) change ide1-cd0 /shared/win-virtio-drivers.iso
  

• Double-check that the changes took effect. KVM-Qemu will not issue an error message in case something went wrong (duh!):

  (qemu) info block
  virtio0: type=hd removable=0 file=/dev/sdb-vol/win7 ro=0 drv=host_device encrypted=0
  ide0-cd0: type=cdrom removable=1 locked=0 file=/shared/win7-eval.iso ro=0 drv=raw encrypted=0
  ide1-cd0: type=cdrom removable=1 locked=0 file=/shared/win-virtio-drivers.iso ro=1 drv=raw encrypted=0
  

Use the “help” command to review the other powerful commands which you can use to tune and debug your running KVM guest (“info”, “migrate” and “system_reset” seem like interesting candidates).

Author: Ivan Zahariev

An experienced Linux & IT enthusiast, Engineer by heart, Systems architect & developer.