The dedicated host shell
When you take out a dedicated host with Bytemark, we provide a login to our dedicated host shell system. This interface provides two functions essential to managing a dedicated host remotely: serial console access and the ability to turn your machine off and on (power cycle).
To log on, you should be in receipt of an SSH key for your dedicated host called (e.g.) joebloggs.key. You need to supply this key to your SSH client instead of a password. The name of the key file identifies your unique dedicated host name on our network, and determines the address to which you’ll need to connect in order to get to your shell:
If you are connecting from a Linux host, the command to use is:
ssh -i joebloggs.dh.key firstname.lastname@example.org
Note ssh insists that the permissions on the keyfile are
0700. If your key
has different permissions you’ll receive a prompt for a passphrase, even if one
has not been set.
With PuTTY on Windows use the
.ppk key e.g.
Once you’ve connected you will see the dedicated host 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.
The serial line will usually show a login prompt unless you have altered your
/etc/inittab to remove it. We don’t recommend this, as the serial 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.
If the server is really wedged, you can use the kernel system request facility
to cause a reboot. To send a system request over the serial line, you send a
break (press Ctrl+p then press b), followed
quickly by one of the Sysrq letters: common ones are S for synchronize
discs, U for unmount discs and B to force a reboot. Others are
documented in the kernel
To exit the serial console press ‘Ctrl-p x’, as indicated by the quick help displayed at the bottom of the window.
dhshell key bindings
dhshell process by default only shows you the serial console of your
machine. There are other functions available which you can access with the
|Ctrl+p [||Scroll backwards|
|Ctrl+p b||Send a break|
|Ctrl+p f||Enter fullscreen mode with no status bars|
|Ctrl+p F||Leave fullscreen mode|
|Ctrl+p h||Read the help|
|Ctrl+p r||Reboot your server|
|Ctrl+p w||Show the watchdog editor|
As the shell is running within GNU Screen you can use most of the standard GNU screen key bindings will work – just note that we’ve changed the prefix from Ctrl+a to Ctrl+p, to avoid confusing when running nested screens.
Power cycling your machine
If your machine is really stuck and you can do nothing else with it then we’d suggest power cycling it. This is not clean and is essentially the same as pulling the plug on your server with no warning.
To power cycle 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. The sequence Ctrl+p s (long power cycle) is similar except this allows the power to be disconnected for up to 60 seconds; it’s useful with some motherboards that seem to have sufficient capacitance to prevent the simple power cycle from working.
You might want to read more about our servers’ booting setup if you need to rescue or reinstall your host from scratch.
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
Take a look at the documentation for the syntax of the rules you can add, and a brief overview of other commands you may run.
You might previously have connected to a different address to access your dedicated host. These were the two we used to advise people to use:
These addresses are specific to the two data centres we host machines within and may stop working in future as we expand the dedicated host shell facilities.
We recommend that you no longer use either of these addresses to avoid future changes.