Add validation in case cgroup2 is not enabled on linux

Author: saville

buildrunner/docker/runner.py

@@ -10,6 +10,7 @@
 import datetime
 import io
 import os.path
+import platform
 import socket
 import ssl
 from collections import OrderedDict
@@ -179,6 +180,14 @@ def start(
             # If we are running in a systemd context, the following 3 settings are necessary to
             # allow services to run.
             if systemd_cgroup2:
+                # Ensure that cgroup v2 is supported before attempting to use it
+                # Note: this check only works on linux systems
+                if platform.system() == "Linux" and not os.path.exists(
+                    "/sys/fs/cgroup/cgroup.controllers"
+                ):
+                    raise BuildRunnerContainerError(
+                        "cgroup v2 is not enabled on this host but is set on the container, please check configuration"
+                    )
                 volumes["/sys/fs/cgroup/buildrunner.scope"] = "/sys/fs/cgroup:rw"
                 tmpfs["/run"] = ""
                 cgroupns = "host"