Quick start on CoreOS Assembler and Fedora CoreOS

cosa

#!/usr/bin/env bash

# this script will use podman, but docker will work too
rpm -qa | grep -q podman || (echo "podman not installed!" ; exit 1)

# checks if cosa image was pulled previously
podman image exists quay.io/coreos-assembler/coreos-assembler || \
  podman pull quay.io/coreos-assembler/coreos-assembler

# create a tmp directory for storing builds
mkdir -p fcos && cd fcos

# define the _real_ cosa command
# https://github.com/coreos/coreos-assembler#define-a-bash-alias-to-run-cosa
cosa() {
   env | grep COREOS_ASSEMBLER
   set -x
   podman run --rm -ti --security-opt label=disable --privileged                                    \
              --uidmap=1000:0:1 --uidmap=0:1:1000 --uidmap 1001:1001:64536                          \
              -v ${PWD}:/srv/ --device /dev/kvm --device /dev/fuse                                  \
              --tmpfs /tmp -v /var/tmp:/var/tmp --name cosa                                         \
              ${COREOS_ASSEMBLER_CONFIG_GIT:+-v $COREOS_ASSEMBLER_CONFIG_GIT:/srv/src/config/:ro}   \
              ${COREOS_ASSEMBLER_GIT:+-v $COREOS_ASSEMBLER_GIT/src/:/usr/lib/coreos-assembler/:ro}  \
              ${COREOS_ASSEMBLER_CONTAINER_RUNTIME_ARGS}                                            \
              ${COREOS_ASSEMBLER_CONTAINER:-quay.io/coreos-assembler/coreos-assembler:latest} "$@"
   rc=$?; set +x; return $rc
}

# run the cosa container and run shell
cosa shell

Instruction for building a FCOS image:

# download the script from gist
# enter the cosa container shell
chmod +x ./cosa && ./cosa

# inside the cosa container
# fetch the Fedora CoreOS configuration
cosa init https://github.com/coreos/fedora-coreos-config

# fetch metadata and packages
cosa fetch

# build the image (qemu on default)
cosa build