There is bunch of lines like:
19:13:29 time="2016-09-12T19:12:23.897547700Z" level=debug msg="Running health check..."
19:13:29 time="2016-09-12T19:12:23.897737700Z" level=debug msg="starting exec command 56c254074d48e5056c45747ca3f8454946d96288ac0fba60cef88a448546626b in container 9003f6182173b76f15a14dcdfce18934483990377dfd316dfdef2aad5c32ff15"
19:13:29 time="2016-09-12T19:12:23.899218000Z" level=debug msg="Health check taking too long"
19:13:29 time="2016-09-12T19:12:23.899277700Z" level=debug msg="attach: stdout: begin"
19:13:29 time="2016-09-12T19:12:23.899333700Z" level=debug msg="attach: stderr: begin"
19:13:29 time="2016-09-12T19:12:23.899363900Z" level=debug msg="attach: stderr: end"
19:13:29 time="2016-09-12T19:12:23.899379700Z" level=debug msg="attach: stdout: end"
19:13:29 time="2016-09-12T19:12:23.900219800Z" level=warning msg="Health check error: rpc error: code = 4 desc = context deadline exceeded"
It seems like it is related to latest containerd update in 6bc9a2d