-# * Docker can be found in the user's path
-# * The user is in the docker group
-# * cgroup is mounted
-# * the docker daemon is running
+function usage {
+ echo >&2
+ echo >&2 "usage: $0 [options]"
+ echo >&2
+ echo >&2 "Calling $0 without arguments will build all Arvados docker images"
+ echo >&2
+ echo >&2 "$0 options:"
+ echo >&2 " -h, --help Print this help text"
+ echo >&2 " clean Clear all build information"
+ echo >&2 " realclean clean and remove all Arvados Docker images except arvados/debian"
+ echo >&2 " deepclean realclean and remove arvados/debian, crosbymichael/skydns and "
+ echo >&2 " crosbymichael/skydns Docker images"
+ echo >&2
+}