Why docker container exits immediately

问题:

I run a container in the background using

 docker run -d --name hadoop h_Service

it exits quickly. But if I run in the foreground, it works fine. I checked logs using

docker logs hadoop

there was no error. Any ideas?

DOCKERFILE

 FROM java_ubuntu_new
 RUN wget http://archive.cloudera.com/cdh4/one-click-install/precise/amd64/cdh4-repository_1.0_all.deb
 RUN dpkg -i cdh4-repository_1.0_all.deb
 RUN curl -s http://archive.cloudera.com/cdh4/ubuntu/precise/amd64/cdh/archive.key | apt-key add -
 RUN  apt-get update
 RUN apt-get install -y hadoop-0.20-conf-pseudo
 RUN dpkg -L hadoop-0.20-conf-pseudo
 USER hdfs
 RUN hdfs namenode -format
 USER root
 RUN apt-get install -y sudo
 ADD . /usr/local/
 RUN chmod 777 /usr/local/start-all.sh
 CMD [\"/usr/local/start-all.sh\"]

start-all.sh

 #!/usr/bin/env bash
 /etc/init.d/hadoop-hdfs-namenode start
 /etc/init.d/hadoop-hdfs-datanode start
 /etc/init.d/hadoop-hdfs-secondarynamenode start
 /etc/init.d/hadoop-0.20-mapreduce-tasktracker start
 sudo -u hdfs hadoop fs -chmod 777 /
 /etc/init.d/hadoop-0.20-mapreduce-jobtracker start
 /bin/bash

回答1:

A docker container exits when its main process finishes.

In this case it will exit when your start-all.sh script ends. I don\'t know enough about hadoop to tell you how to do it in this case, but you need to either leave something running in the foreground or use a process manager such as runit or supervisord to run the processes.

I think you must be mistaken about it working if you don\'t specify -d; it should have exactly the same effect. I suspect you launched it with a slightly different command or using -it which will change things.

A simple solution may be to add something like:

while true; do sleep 1000; done

to the end of the script. I don\'t like this however, as the script should really be monitoring the processes it kicked off.

(I should say I stole that code from https://github.com/sequenceiq/hadoop-docker/blob/master/bootstrap.sh)

回答2:

This did the trick for me:

docker run -dit ubuntu

After it, I checked for the processes running using:

docker ps -a

For attaching again the container

docker attach CONTAINER_NAME

TIP: For exiting without stopping the container type: ^P^Q

回答3:

I would like to extend or dare I say, improve answer mentioned by camposer

When you run

docker run -dit ubuntu

you are basically running the container in background in interactive mode.

When you attach and exit the container by CTRL+D (most common way to do it), you stop the container because you just killed the main process which you started your container with the above command.

Making advantage of an already running container, I would just fork another process of bash and get a pseudo TTY by running:

docker exec -it <container ID> /bin/bash

回答4:

whenever I want a container to stay up after finish the script execution I add

&& tail -f /dev/null

at the end of command. So it should be:

/usr/local/start-all.sh && tail -f /dev/null

回答5:

A nice approach would be to start up your processes and services running them in the background and use the wait [n ...] command at the end of your script. In bash, the wait command forces the current process to:

Wait for each specified process and return its termination status. If n is not given, all currently active child processes are waited for, and the return status is zero.

I got this idea from Sébastien Pujadas\' start script for his elk build.

Taking from the original question, your start-all.sh would look something like this...

 #!/usr/bin/env bash
 /etc/init.d/hadoop-hdfs-namenode start &
 /etc/init.d/hadoop-hdfs-datanode start &
 /etc/init.d/hadoop-hdfs-secondarynamenode start &
 /etc/init.d/hadoop-0.20-mapreduce-tasktracker start &
 sudo -u hdfs hadoop fs -chmod 777 /
 /etc/init.d/hadoop-0.20-mapreduce-jobtracker start &
 wait

回答6:

My pracitce is in the Dockerfile start a shell which will not exit immediately CMD [ \"sh\", \"-c\", \"service ssh start; bash\"], then run docker run -dit image_name. This way the (ssh) service and container is up running.

回答7:

Adding

exec \"$@\"

at the end of my shell script was my fix!

回答8:

There are many possible ways to cause a docker to exit immediately. For me, it was the problem with my Dockerfile. There was a bug in that file. I had ENTRYPOINT [\"dotnet\", \"M4Movie_Api.dll] instead of ENTRYPOINT [\"dotnet\", \"M4Movie_Api.dll\"]. As you can see I had missed one quotation(\") at the end.

To analyze the problem I started my container and quickly attached my container so that I could see what was the exact problem.

C:\\SVenu\\M4Movie\\Api\\Api>docker start 4ea373efa21b


C:\\SVenu\\M4Movie\\Api\\Api>docker attach 4ea373efa21b

Where 4ea373efa21b is my container id. This drives me to the actual issue.

After finding the issue, I had to build, restore, publish my container again.

回答9:

You can run the container using this restart flag.

docker run -d --name=<some-name> -p xxxx:xxxx ... <image-name> --restart=unless-stopped

回答10:

Since the image is a linux, one thing to check is to make sure any shell scripts used in the container have unix line endings. If they have a ^M at the end then they are windows line endings. One way to fix them is with dos2unix on /usr/local/start-all.sh to convert them from windows to unix. Running the docker in interactive mode can help figure out other problems. You could have a file name typo or something. see https://en.wikipedia.org/wiki/Newline