Sorry, but I can’t figure out how to use it:
$ docker run --name mycont4 ubuntu echo one
one
$ docker exec mycont4 echo two
2014/11/10 13:24:06 Error response from daemon: Container mycont4 is not running
$ docker start mycont4
mycont4
$ docker exec mycont4 echo two
2014/11/10 13:24:24 Error response from daemon: Container mycont4 is not running
$