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BackFor Worst-Case Scenarios: Rescue Mode with Grml
For your servers at cloudscale, you can choose from a range of popular Linux distributions, but you have also had the option for a while now of starting other operating systems. The most common reason for booting a system other than the pre-installed one is probably to resolve problems. Here, the new rescue mode for your servers helps you avoid numerous steps so that, in the worst-case scenario, you can get your server back online as quickly as possible.
Rescue mode as an additional boot option
You can use the VNC console to start your servers from a volume other than the root volume, which will allow you to boot and, if required, install almost any operating system. However, first of all you need to attach an additional volume to your server with the required content for booting (e.g. a USB or ISO image). Although this process offers you complete flexibility, it can cost precious time in an emergency.
Rescue mode now offers you a multifunctional tool that is available at all times in such cases. It takes just two clicks for your server to start a Grml image. This Debian-based distribution can probably be considered as the standard live image for tricky situations.
A live system is particularly helpful when normal access to your server is not working for whatever reason. Whether the server is not booting in the first place (the reason for this can often be seen in the console log), cannot access the network properly, has an excessively restrictive firewall setting, or you have simply lost the login details, Grml (in the same way as the boot diskette used to) offers you a tool to access a faulty configuration and solve the problem.
Activate rescue mode
You activate rescue mode via the blue "emergency suitcase" button in the cloud control panel. When you activate rescue mode, your server automatically restarts or switches on and then boots the Grml live image. You can then use the VNC console to access your server and, if required, open e.g. network access or mount the root volume.
Grml offers you a wealth of options from the outset. If you let the 30-second countdown of the boot loader elapse, it starts with the default settings and then offers you a selection menu via the VNC console where you can, for example, change the keyboard layout or network configuration. By pressing "q", you reach the zsh shell and can decide for yourself what to do next.
More features for faster work
You can work in a more targeted – and convenient – manner if you provide the boot loader with information. Press the Tabulator key during the countdown and add options to the displayed string, e.g. services=networking,cloud-init-main,cloud-config,ssh, followed by the Enter key. This will enable Grml to activate the network while booting (it obtains the settings via DHCP) and to load the SSH daemon.
Most importantly, however, it also starts "cloud-init"; this obtains, among other things, the SSH public keys that you selected when creating the server from our metadata server and stores them for the "grml" live user. This means that you can access the server straight away with ssh grml@<IP address> and will have all the usual SSH options, including copy/paste from your local system and file transfers.
Grml offers you a wide range of aids and short-cuts. In order to obtain an overview, use grml-tips <keyword> directly in the Grml zsh on your server and have a look at the cheat codes on the Grml website.
Back to normal operation
Once you are ready, you deactivate rescue mode again via the control panel. The server restarts and boots from its root volume as usual. If the error was successfully eliminated, you can then access your server as normal, e.g. via SSH with your standard username and SSH key.
While rescue mode is active, you can reboot or switch off the server, e.g. with the shutdown command. Before you do so, be aware that a switched-off server in rescue mode can only be switched on again by deactivating rescue mode (the reason for this is a specific trait of OpenStack, which our cloud infrastructure is based on). The server will then once again try to boot from its root volume, although you still have the option of activating rescue mode again.
We all know that things sometimes get stuck in IT. The new rescue mode for your servers at cloudscale means that you can get to where it matters more quickly, for example to the decisive config that gets everything up and running again.
The right tool when it matters!
Your cloudscale team