The Virtual Machine Shell

When you take out a virtual machine Bytemark, we provide a login to our shell system. This interface provides two functions essential to managing a remote host remotely: serial console access and the ability to turn your machine off and on (power cycle).

The shell interface

Once you’ve connected you will see the shell interface, allowing you to immediately see the output of the serial console of your machine and call up the other functions.

The display should look something like this:

Note the two status lines at the bottom remove two lines from your terminal size. If you run editors or other full-screen applications and want to avoid the odd bit of corruption, you may want to expand your terminal by two lines to compensate or see the key-strokes section below for details of how to remove them.

The console will usually show a login prompt unless you have altered your ‘/etc/inittab’ to remove it. We don’t recommend this, as this login is your primary means of fixing a broken network or firewall. You will also see kernel messages printed here; this is where to look for messages indicating disc failure or excessive network activity.

If you don’t see a login prompt straight away you may need to press return a couple of times. Recent Ubuntu versions have changes the way serial line access is configured; this is of particular interest if you do an upgrade from hardy or jaunty – there is information about this here

To exit the serial console press ‘Ctrl-p x’, as indicated by the quick help displayed at the bottom of the window.

Keybindings

The dhshell process by default only shows you the serial console of your machine. There are other functions available which you can access with the following keys:

As the shell is running within GNU Screen you can use most of the standard GNU screen keybindings will work – just note that we’ve changed the prefix from ‘Ctrl-a’ to ‘Ctrl-p’, to avoid confusing when running nested screens.

PowerCycling Your Machine

If your machine is really stuck and you can do nothing else with it then we’d suggest powercycling it. This is not clean and is essentially the same as pulling the plug on your server with no warning.

To powercycle your machine press ‘Ctrl-p r’ and confirm your decision. The machine should then reboot, and after a few seconds you’ll be able to see the serial console output our boot loader messages.

Using the watchdog

You can also set up watchdog checks in exactly the same way as for virtual machines.

To open the watchdog interface press ‘Ctrl-p w’. This will open up a new window which allows you to enter watchdog commands, once you’ve finished you can close it by entering ‘exit’.