add current limitation to experimental/checkpoint-restore.md
@@ -71,5 +71,17 @@ in between running/checkpoint/restoring you should see that the counter
increases while the process is running, stops while it's checkpointed, and
resumes from the point it left off once you restore.
-Note that seccomp is only supported by CRIU in very up to date kernels.
+## Current Limitation
+
+seccomp is only supported by CRIU in very up to date kernels.
+
+External terminal (i.e. `docker run -t ..`) is not supported at the moment.
+If you try to create a checkpoint for a container with an external terminal,
+it would fail:
+
+ $ docker checkpoint create cr checkpoint1
+ Error response from daemon: Cannot checkpoint container c1: rpc error: code = 2 desc = exit status 1: "criu failed: type NOTIFY errno 0\nlog file: /var/lib/docker/containers/eb62ebdbf237ce1a8736d2ae3c7d88601fc0a50235b0ba767b559a1f3c5a600b/checkpoints/checkpoint1/criu.work/dump.log\n"
+
+ $ cat /var/lib/docker/containers/eb62ebdbf237ce1a8736d2ae3c7d88601fc0a50235b0ba767b559a1f3c5a600b/checkpoints/checkpoint1/criu.work/dump.log
+ Error (mount.c:740): mnt: 126:./dev/console doesn't have a proper root mount
