Building a Kernel

Compiling your own Linux is not actually that hard. You will want to do this if the hello-world kernel provided by Firecracker lacks options you need or if you want to use a newer kernel version. This documentation is adapted from the Firecracker developer guide. We recommend using the v5.12 kernel configuration we provide in the ./kernel directory.

You need three things:

1. Kernel sources
2. A tool chain
3. A configuration file

You can get the kernel sources by cloning the Linux repository:

# warning! this is about 3.5GB in size so sit back and wait
git clone https://github.com/torvalds/linux.git linux.git
cd linux.git

# then checkout the version you want, e.g. v4.19
git checkout v4.19

You also need a few things for your tool chain. The details depend on your distribution, here are the packages needed on Ubuntu 18.04:

sudo apt-get install build-essential linux-source bc kmod cpio flex \
    libncurses5-dev libelf-dev libssl-dev bison -y

Finally, your config file is used to configure your kernel. We recommend our ./kernel/config-5.12 for the v5.12 configuration. You should name your config file .config and place it in the linux.git folder.

You can modify this configuration with the menuconfig tool:

make menuconfig

Save your configuration and build your kernel with:

make vmlinux

Pro-tip: use make vmlinux -j [NO_THREADS] to multi-thread your compilation.

This takes a few minutes. There you go, now you have your vmlinux file that you can use as a kernel.

If you want to use Docker within your microVM, you need to build a kernel that has support for everything Docker requires. Check out this repository for information on how to do that.