docker attach vs lxc-attach

Question

UPDATE: Docker 0.9.0 use libcontainer now, diverting from LXC see: Attaching process to Docker libcontainer container

I'm running an istance of elasticsearch:

docker run -d -p 9200:9200 -p 9300:9300 dockerfile/elasticsearch

Checking the process it show like the following:

$ docker ps --no-trunc
CONTAINER ID                                                       IMAGE                             COMMAND                                           CREATED             STATUS              PORTS                                            NAMES
49fdccefe4c8c72750d8155bbddad3acd8f573bf13926dcaab53c38672a62f22   dockerfile/elasticsearch:latest   /usr/share/elasticsearch/bin/elasticsearch java   About an hour ago   Up 8 minutes        0.0.0.0:9200->9200/tcp, 0.0.0.0:9300->9300/tcp   pensive_morse   

Now, when I try to attach the running container, I get stacked:

$  sudo docker attach 49fdccefe4c8c72750d8155bbddad3acd8f573bf13926dcaab53c38672a62f22
[sudo] password for lsoave:

the tty doesn't connect and the prompt is not back. Doing the same with lxc-attach works fine:

$ sudo lxc-attach -n 49fdccefe4c8c72750d8155bbddad3acd8f573bf13926dcaab53c38672a62f22
root@49fdccefe4c8:/# ps -ef
UID        PID  PPID  C STIME TTY          TIME CMD
root         1     0 49 20:37 ?        00:00:20 /usr/bin/java -Xms256m -Xmx1g -Xss256k -Djava.awt.headless=true -XX:+UseParNewGC -XX:+UseConcMa
root        88     0  0 20:38 ?        00:00:00 /bin/bash
root        92    88  0 20:38 ?        00:00:00 ps -ef
root@49fdccefe4c8:/# 

Does anybody know what's wrong with docker attach ?

NB. dockerfile/elasticsearch ends with:

ENTRYPOINT ["/usr/share/elasticsearch/bin/elasticsearch"]

Answer 1

You're attaching to a container that is running elasticsearch which isn't an interactive command. You don't get a shell to type in because the container is not running a shell. The reason lxc-attach works is because it's giving you a default shell. Per man lxc-attach:

If no command is specified, the current default shell of the user running lxc-attach will be looked up inside the container and executed. This will fail if no such user exists inside the container or the container does not have a working nsswitch mechanism.

docker attach is behaving as expected.