Running on kernel versions older than 3.10 has not been
supported for a while (as it's known to be unstable).
With the containerd integration, this has become more
apparent, because kernels < 3.4 don't support PR_SET_CHILD_SUBREAPER,
which is required for containerd-shim to run.
Change the previous "warning" to a "fatal" error, so
that we refuse to start.
There's still an escape-hatch for users by setting
"DOCKER_NOWARN_KERNEL_VERSION=1" so that they can
run "at their own risk".
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
Upstream-commit: 51b23d88422918c24291f5876df35f91b23a446a
Component: engine
1cc08f7023