Running your KVM virtual machines headless in a data center environment using the built in vnc server is a neat feature of KVM but what happens when you want to access your monitor from across the network? Well, it turns out there’s an option for redirecting your monitor to tcp sockets and there are two methods of doing this.

The tcp options

There are two basic options for redirecting your monitor to tcp sockets, namely raw socket and using the telnet protocol. I’ll go ahead and show the syntax for both options then discuss the options you have. For redirecting your monitor to raw tcp socket you use the following syntax:

-monitor tcp:192.168.1.1:4444,server,nowait 

For redirecting to a socket supporting telnet protocol you use the following syntax

-monitor telnet:192.168.1.1:4444,server,nowait

The options are

• tcp – raw tcp sockets
• telnet – the telnet protocol is used instead of raw tcp sockets. This is the preferred option over tcp as you can break out of the monitor using Ctrl-] then typing quit. You can’t break out of the monitor like this after connecting with the raw socket option
• 192.168.1.1 – Listen on this port only. You can use 127.0.0.1 if you want to only allow connections locally. If you want to listen on any ip address on the server, just leave this blank so you end up with two consecutive colons ie “::” .
• 4444 – port number to listen on.
• server – listening in server mode
• nowait – qemu will wait for a client socket application to connect to the port before continuing unless this option is used. In most cases you’ll want to use the nowait option.

An example

So as an example for your typical case where you have your headless kvm virtual machine running with a vnc server and want to access the monitor from across the network, you’d probably want to use the following command to start your virtual machine.

qemu-system-x86_64 –m 400 –hda windows.img –usbdevice tablet –vnc :1 –monitor  telnet:192.168.1.100:4444,server,nowait 

If you’re going to be listening on any ip addresses on your server, you can also use

qemu-system-x86_64 –m 400 –hda windows.img –usbdevice tablet –vnc :1 –monitor  telnet::4444,server,nowait 

Now in order to access your virtual machine monitor from across the network you would type the following

telnet 192.168.1.100 4444

This would give you access to your monitor remotely. To close and break out of the monitor you simply type Ctrl-] to get the telnet prompt then type quit. If you don't type the Ctrl-] followed by quit and only type the quit command, you'll kill your virtual machine ungracefully. If you have security on your virtual machine host server such as ssh, then you can either ssh to the host server then telnet to localhost or use ssh tunneling.

So next time you’re thinking about running headless kvm machines and wondering how to manage them remotely you have two more options.