-# build the Docker images
-docker build -t arvados/base base
-docker build -t arvados/api api
+# Check that:
+# * IP forwarding is enabled in the kernel.
+
+if [ "$(/sbin/sysctl --values net.ipv4.ip_forward)" != "1" ]
+then
+ echo >&2 "WARNING: IP forwarding must be enabled in the kernel."
+ echo >&2 "Try: sudo sysctl net.ipv4.ip_forward=1"
+ build_ok=false
+fi
+
+# * Docker can be found in the user's path
+# * The user is in the docker group
+# * cgroup is mounted
+# * the docker daemon is running
+
+if ! docker images > /dev/null 2>&1
+then
+ echo >&2 "WARNING: docker could not be run."
+ echo >&2 "Please make sure that:"
+ echo >&2 " * You have permission to read and write /var/run/docker.sock"
+ echo >&2 " * a 'cgroup' volume is mounted on your machine"
+ echo >&2 " * the docker daemon is running"
+ build_ok=false
+fi
+
+# * config.yml exists
+if [ '!' -f config.yml ]
+then
+ echo >&2 "WARNING: no config.yml found in the current directory"
+ echo >&2 "Copy config.yml.example to config.yml and update it with settings for your site."
+ build_ok=false
+fi
+
+# If ok to build, then go ahead and run make
+if $build_ok
+then
+ make $*
+fi