Script to set up Flatcar to run on firecracker. Run in an empty directory to download all components, then run ./start-flatcar.sh to run Flatcar on Firecracker.

flatcar-on-firecracker.sh

#!/bin/bash

set -eu

function get_firecracker() {
    rm -f firecracker-v0.24.6-x86_64.tgz firectl-v0.1.0
    rm -rf release-*/*

    wget https://github.com/firecracker-microvm/firecracker/releases/download/v0.24.6/firecracker-v0.24.6-x86_64.tgz
    wget https://firectl-release.s3.amazonaws.com/firectl-v0.1.0
    tar xzf firecracker-v0.24.6-x86_64.tgz
    mv release-*/* .
    chmod 755 firecracker-* firectl-*
}
# --

function get_flatcar() {
    local i
    for i in "flatcar_production_image.bin.bz2" \
             "flatcar_production_image.vmlinuz" ; do
        wget "https://stable.release.flatcar-linux.net/amd64-usr/current/$i"
    done

    bunzip2 flatcar_production_image.bin.bz2
}
# --

function extract_vmlinux() {
    wget https://raw.githubusercontent.com/torvalds/linux/master/scripts/extract-vmlinux
    chmod 755 extract-vmlinux

    patch -p0 <<EOF
--- extract-vmlinux 2021-11-05 14:28:47.123984433 +0100
+++ extract-vmlinux 2021-11-05 14:28:29.487982001 +0100
@@ -49,12 +49,17 @@
 trap "rm -f \$tmp" 0
  
 # That didn't work, so retry after decompression.
-try_decompress '\\037\\213\\010' xy    gunzip
-try_decompress '\\3757zXZ\\000' abcde unxz
-try_decompress 'BZh'          xy    bunzip2
-try_decompress '\\135\\0\\0\\0'   xxx   unlzma
-try_decompress '\\211\\114\\132' xy    'lzop -d'
-try_decompress '\\002!L\\030'   xxx   'lz4 -d'
+#try_decompress '\\037\\213\\010' xy    gunzip
+#try_decompress '\\3757zXZ\\000' abcde unxz
+#try_decompress 'BZh'          xy    bunzip2
+#try_decompress '\\135\\0\\0\\0'   xxx   unlzma
+#try_decompress '\\211\\114\\132' xy    'lzop -d'
+#try_decompress '\\002!L\\030'   xxx   'lz4 -d'
+
+# check if unzstd is installed, fail if it is not
+set -e
+unzstd -V >/dev/null
+set +e
 try_decompress '(\\265/\\375'   xxx   unzstd
           
 # Finally check for uncompressed images or objects:
EOF
    ./extract-vmlinux flatcar_production_image.vmlinuz > flatcar-vmlinux
}

get_firecracker

firecracker="$(echo ./firecracker-*)"
firectl="$(echo ./firectl-*)"

get_flatcar

extract_vmlinux

verity_hash="$(dd if=flatcar_production_image.vmlinuz conv=notrunc skip=64 count=64 bs=1 status=none)"
root_uuid=$(partx -s flatcar_production_image.bin | grep ROOT | tr -s " " | cut -d " " -f 8)
usr_uuid=$(partx -s flatcar_production_image.bin | grep USR-A | tr -s " " | cut -d " " -f 8)

echo "${firectl} --firecracker-binary=${firecracker} \
           --kernel=flatcar-vmlinux --root-drive=flatcar_production_image.bin \
           --root-partition=$root_uuid \
           --kernel-opts='rootflags=rw mount.usrflags=ro BOOT_IMAGE=/flatcar/vmlinuz-a mount.usr=/dev/mapper/usr verity.usr=PARTUUID=$usr_uuid consoleblank=0 console=ttyS0,115200n8 console=tty0 flatcar.autologin verity.usrhash=$verity_hash rd.driver.pre=virtio_mmio console=ttyS0 reboot=k panic=1 i8042.noaux i8042.nomux i8042.nopnp i8042.dumbkbd'" > start-flatcar.sh
chmod 755 start-flatcar.sh

echo
echo " All done - run ./start-flatcar.sh to run Flatcar on Firecracker."