问题
I can run an ubuntu container successfully:
# docker run -it -d ubuntu
3aef6e642327ce7d19c7381eb145f3ad10291f1f2393af16a6327ee78d7c60bb
# docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
3aef6e642327 ubuntu "/bin/bash" 3 seconds ago Up 2 seconds condescending_sammet
But executing docker attach hangs:
# docker attach 3aef6e642327
Until I press any key, such as Enter:
# docker attach 3aef6e642327
root@3aef6e642327:/#
root@3aef6e642327:/# ls
bin boot dev etc home lib lib64 media mnt opt proc root run sbin srv sys tmp usr var
Why does docker attach hang?
Update:
After reading the comments, I think I get the answers:
prerequisite:
"docker attach" reuse the same tty, not open new tty.
(1) Executing the docker run without daemon mode:
# docker run -it ubuntu
root@eb3c9d86d7a2:/#
Everything is OK, then run ls command:
root@eb3c9d86d7a2:/# ls
bin boot dev etc home lib lib64 media mnt opt proc root run sbin srv sys tmp usr var
root@eb3c9d86d7a2:/#
(2) Run docker run in daemon mode:
# docker run -it -d ubuntu
91262536f7c9a3060641448120bda7af5ca812b0beb8f3c9fe72811a61db07fc
Actually, the following should have been outputted to stdout from the running container:
root@91262536f7c9:/#
So executing docker attach seems to hang, but actually it is waiting for your input:
# docker attach 91262536f7c9
ls
bin boot dev etc home lib lib64 media mnt opt proc root run sbin srv sys tmp usr var
root@91262536f7c9:/#
回答1:
It does not really hang. As you can see in the comment below (You are running "/bin/bash" as command) it seems to be expected behaviour when attaching.
As far as I understand you attach to the running shell and just the stdin/stdout/stderr - depending on the options you pass along with the run command - will just show you whatever goes in/out from that moment. (Someone with a bit more in-depth knowledge hopefuly can explain this on a higher level).
As I wrote in my comment on your question, there are several people who have opened an issue on the docker github repo describing similar behaviour:
- docker attach [container] hangs, requires input #8521
- docker attach hangs setting terminal state when attaching to container
Since you mention shell, I assume you have a shell already running. attach doesn't start a new process, so what is the expected behavior of connecting to the in/out/err streams of a running process? I didn't think about this. Of course this is the expected behavior of attaching to a running shell, but is it desirable?
Would it be at all possible to flush stdout/stderr on docker attach thereby forcing the shell prompt to be printed or is it a bit more complex than that? That's what I personally would "expect" when attaching to an already running shell.
Feel free to close this issue if necessary, I just felt the need to document this and get some feedback.
- Taken from a comment on this github issue. You can find more insight in the comments of this issue.
If instead of enter you would start typing a command, you would not see the extra empty prompt line. If you were to run
$ docker exec -it ubuntu <container-ID-or-name> bash
where <container-ID-or-name> is the ID or name of the container after you run docker run -it -d ubuntu (so 3aef6e642327 or condescending_sammet in your question) it would run a new command, thus not having this "stdout problem" of attaching to an existing one.
Example
If you would have a Dockerfile in a directory containing:
FROM ubuntu:latest
ADD ./script.sh /timescript.sh
RUN chmod +x /timescript.sh
CMD ["/timescript.sh"]
And have a simple bash script script.sh in the same directory containing:
#!/bin/bash
#trap ctrl-c and exit, couldn't get out
#of the docker container once attached
trap ctrl_c INT
function ctrl_c() {
exit
}
while true; do
time=$(date +%N)
echo $time;
sleep 1;
done
Then build (in this example in the same directory as the Dockerfile and script.sh) and run it with
$ docker build -t nan-xiao/time-test .
..stuff happening...
$ docker run -itd --name time-test nan-xiao/time-test
Finally attach
$ docker attach time-test
You will end up attached to a container printing out the time every second. (CTRL-C to get out)
Example 2
Or if you would have a Dockerfile containing for example the following:
FROM ubuntu:latest
RUN apt-get -y install irssi
ENTRYPOINT ["irssi"]
Then run in the same directory:
$ docker build -t nan-xiao/irssi-test .
Then run it:
$ docker run -itd --name irssi-test nan-xiao/irssi-test
And finally
$ docker attach irssi-test
You would end up in a running irssi window without this particular behaviour. Of course you can substitute irrsi for another program.
回答2:
I ran into this issue as well when attempting to attach to a container that was developed by someone else and already running a daemon. (In this case, it was LinuxServer's transmission docker image).
Problem:
What happened was the terminal appeared to 'hang', where typing anything didn't help and wouldn't show up. Only Ctrl-C would kick me back out.
docker run, docker start, docker attach all was not successful, turns out the command I needed (after the container has been started with run or start) was to execute bash, as chances are the container you pulled from doesn't have bash already running.
Solution:
docker exec -it <container-id> bash
(you can find the container-id from running docker ps -a).
This will pull you into the instance with a functional bash as root (assuming there was no other explicit set up done by the image you pulled).
I know the accepted answer has captured this as well, but decided to post another one that is a little more terse and obvious, as the solution didn't pop out for me when I was reading it.
回答3:
This happened to me once for the following reason:
It could be that the bash command inside the container is executing a "cat" command.
So when you attach to the container (the bash command) you are actualy inside the cat command which is expecting input. (text and/or ctrl-d to write the file)
回答4:
When I run docker attach container-name, then nothing output, even Ctrl-c is invalid. So, first try
docker attach container-name --sig-proxy=false
and then ctrl-c can stop it. Why it didn't output anything?
just because the container doesn't output. Actually I need to enter my container and run some shell command. So the correct command is
docker exec -ti container-name bash
回答5:
If you cannot access command line, just make sure you run your container with -i flag at start.
回答6:
I just had a similar problem today and was able to fix it:
Here is what was happening for me:
docker-compose logs -f nginx
Attaching to laradock_nginx_1
Then it would hang there until I quit via CTRL-C: ^CERROR: Aborting.
docker ps -a showed that what SHOULD have been called laradock_nginx did not exist with that Image Name, so I figured I'd just remove and re "up" that container:
docker stop cce0c32f7556
docker rm cce0c32f7556
docker-compose up -d laradock_nginx
Unfortunately: ERROR: No such service: laradock_nginx
So I did a sudo reboot and then docker ps -a, but laradock_nginx still wasn't there.
Luckily, docker-compose up -d nginx then worked and docker-compose logs -f nginx now works.
来源：https://stackoverflow.com/questions/35573698/why-does-docker-attach-hang