It's probably better to use the server tags that Scaleway provides to specify your KEXEC_KERNEL and KEXEC_INITRD, rather than the scripts provided here. The fstab and udev rules in this repository might still be useful in getting a working system running.

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Custom Kernel Launcher for Scaleway

A collection of scripts to load a custom kernel on Scaleway servers

Disclaimer

This project is not affiliated with nor endorsed by Scaleway or Online SAS in any way.

Scaleway is a trademark of Online SAS.

Introduction

The virtual (i.e. not-baremetal) servers available on Scaleway are run within KVM. In theory, this gives you a proper virtual machine that you can do whatever you wish within.

However, there currently is no official support for booting a custom kernel, as might be necessary for some more obscure or very new features, or custom patches.

Luckily, Scaleway has kindly enabled kexec on their servers. This lets us replace the currently running kernel with another one.

With a couple of scripts, we can get this to automatically happen on boot, which gives us a pretty seamless way to get into a custom kernel.

Supported platforms

Currently, this is written for the official Scaleway Ubuntu 16.04 image and tested on a VC1S, VC1M and X64-15GB. It might need some tweaking for other distros, or for use on the baremetal servers.

Instructions

You are expected to be running as root. The install scripts are written for a clean image, and might overwrite other settings.

1. Clone this repository somewhere.

2. Install a custom or distro-official kernel. In Ubuntu, this can be accomplished with apt install linux-generic. You are expected to end up with a /vmlinuz and /initrd.img file in the root. If it prompts you, do not install grub on any devices - leave them all unticked and press enter, then yes continue without installing grub.

3. Install kexec. In Ubuntu, apt install kexec-tools. If it prompts you, you do not want it to handle reboots.

4. Run install.sh. This will copy some configs necessary to get prevent errors during the boot.

5. Run uname -r and record the output. This is your old (Scaleway) kernel.

6. Test by running systemctl kexec, which should switch into the new kernel. You will need to reconnect.

7. Check uname -r again -- you should now be in your new (custom) kernel.

8. If the manual reboot worked, you can enable auto-switch on boot by running enable-autostart.sh. If it did not work, I would recommend figuring out why first so you do not get stuck in an unbootable system.

Details

This is mostly based off the simple kexec commands described on the Archlinux wiki. There are some adjustments:

• /etc/fstab needs an entry added to set the root filesystem to rw, otherwise it's in readonly.

• /etc/udev/rules.d needs a config that sets the network interface to eth0, since the Ubuntu kernel by default uses a different naming scheme. Alternative methods include either disabling the new naming by setting net.ifnames=0 in the kernel command line (--append arg on kexec) or changing the interface name away from eth0 in /etc/network/interfaces.

• Some systemd entries are added to load the correct image (edit /etc/systemd/system/sckl-kexec-load.service to change the kexec command line) and to run it on boot if enabled (the trigger service).

• A systemd override is applied to disable the Scaleway scw-generate-ssh-keys.service, which otherwise errors on startup. It's supposed to be a one-off generation anyway so hopefully not too important.

Other platforms

I expect this to work on all the VPSes. If you're using it on the baremetal servers, you might need to configure the root device in /etc/fstab, since it's probaby not /dev/vda... The network interface in the udev rule also needs to be updated, since it's currently pinned to the KVM virtio name.

For other distros, you might need to customise the systemd scripts appropriately. The network interface rules might also need to be updated.