I was wondering if anyone knew if it is possible to know when a docker CMD is done executing?
I initially have tried putting an ENTRYPOINT command after the CMD but it runs immediately when you run the docker container.
Also, if this can only be done with docker-compose that would be fine as well if there is a way to know when the command: is finished?
The container stops and exits once the CMD has finished running.
You can use:
$ docker wait [container name/id]
to wait on a container to stop. If the container is already stopped, this command will return immediately. Otherwise, it'll wait until the container finishes its work, or is otherwise stopped.
From https://docs.docker.com/engine/reference/commandline/wait/
Block until one or more containers stop, then print their exit codes
The Docker CMD will not be done until the container is stopped/killed. The CMD instruction is a way start the main process that will run inside the container. This process will keep running until the
container is stopped or killed.
Inside the Dockerfile, it doesn't matter where you put the CMD or ENTRYPOINT instruction. When you include both and ENTYPOINT and CMD instructions inside the same dockerfile, the CMD will be appended to the ENTRYPOINT command as arguments.
The first two answers are indeed correct but don't directly answer your questions. Once the CMD is finished the container will exit, but will still exist on your host until it's removed.
Assuming you started the docker run or docker-compose up with a -d so that they run in the background (detached):
docker container ps only shows running containers, so once it's exited then docker container ps -a will show it.
docker-compose ps shows the status of all compose services, including stopped containers.
I am running a docker container which is trying to access a port in another docker container. Both of these are running are configured together to run on the same network. But as soon as I start this container it gets killed and doesn't throw any error. There are no error logs. I also tried using docker inspect but couldn't find much.
PS: I am a newbie docker user.
Following from OP comment w/ ENTRYPOINT
ENTRYPOINT /configure.sh && bash
Answer
Given your ENTRYPOINT the container will always exit since the process is bash. You need to have a continuously running process in the foreground for the container to stay running i.e. an application daemon.
Here is my simple docker file
FROM java:8
EXPOSE 4000
now when I run it using the following command
sudo docker run --name hello dockerfile
and do docker ps -a it shows the status as exited. I just want to keep this container up and running so I can ssh into this container and probably transfer files and so on. It looks like containers are mainly used to run servers am I correct?
you can at least keep your container up with something like docker run -d hello sleep infinity but as said by René M, you should put in your Dockerfile something to do in your CMD or ENTRYPOINT, see the doc
https://docs.docker.com/engine/reference/builder/#cmd
and
https://docs.docker.com/engine/reference/builder/#entrypoint
That is realy simple.
Because your container is running nothing that last long. What happens is, that this container starts, has nothing to do and stops.
What you can do is:
Run the container in interactive mode with attached tty. This way your console enters the container after it's start, and let him run a tty, which is something to do and prevends the container from stopping. Then you can work inside this container, like installing an application. Doing this your work will be lost after stoping the container. But you can run docker commit on that container, which makes your changes persistent.
docker run -i -t --name hello dockerfile
Enhance your dockerfile with something usefull. Like copying an application into the container and provide a CMD command to run, when the container starts.
After this the container will last as long as your CMD command runs. If the command is a server or deamon application, the container will last for ever and will only stop when you stop him.
I've seen a bunch of tutorials that seem do the same thing I'm trying to do, but for some reason my Docker containers exit. Basically, I'm setting up a web-server and a few daemons inside a Docker container. I do the final parts of this through a bash script called run-all.sh that I run through CMD in my Dockerfile. run-all.sh looks like this:
service supervisor start
service nginx start
And I start it inside of my Dockerfile as follows:
CMD ["sh", "/root/credentialize_and_run.sh"]
I can see that the services all start up correctly when I run things manually (i.e. getting on to the image with -i -t /bin/bash), and everything looks like it runs correctly when I run the image, but it exits once it finishes starting up my processes. I'd like the processes to run indefinitely, and as far as I understand, the container has to keep running for this to happen. Nevertheless, when I run docker ps -a, I see:
➜ docker_test docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
c7706edc4189 some_name/some_repo:blah "sh /root/run-all.sh 8 minutes ago Exited (0) 8 minutes ago grave_jones
What gives? Why is it exiting? I know I could just put a while loop at the end of my bash script to keep it up, but what's the right way to keep it from exiting?
If you are using a Dockerfile, try:
ENTRYPOINT ["tail", "-f", "/dev/null"]
(Obviously this is for dev purposes only, you shouldn't need to keep a container alive unless it's running a process eg. nginx...)
I just had the same problem and I found out that if you are running your container with the -t and -d flag, it keeps running.
docker run -td <image>
Here is what the flags do (according to docker run --help):
-d, --detach=false Run container in background and print container ID
-t, --tty=false Allocate a pseudo-TTY
The most important one is the -t flag. -d just lets you run the container in the background.
This is not really how you should design your Docker containers.
When designing a Docker container, you're supposed to build it such that there is only one process running (i.e. you should have one container for Nginx, and one for supervisord or the app it's running); additionally, that process should run in the foreground.
The container will "exit" when the process itself exits (in your case, that process is your bash script).
However, if you really need (or want) to run multiple service in your Docker container, consider starting from "Docker Base Image", which uses runit as a pseudo-init process (runit will stay online while Nginx and Supervisor run), which will stay in the foreground while your other processes do their thing.
They have substantial docs, so you should be able to achieve what you're trying to do reasonably easily.
you can run plain cat without any arguments as mentioned by bro #Sa'ad to simply keep the container working [actually doing nothing but waiting for user input] (Jenkins' Docker plugin does the same thing)
The reason it exits is because the shell script is run first as PID 1 and when that's complete, PID 1 is gone, and docker only runs while PID 1 is.
You can use supervisor to do everything, if run with the "-n" flag it's told not to daemonize, so it will stay as the first process:
CMD ["/usr/bin/supervisord", "-n"]
And your supervisord.conf:
[supervisord]
nodaemon=true
[program:startup]
priority=1
command=/root/credentialize_and_run.sh
stdout_logfile=/var/log/supervisor/%(program_name)s.log
stderr_logfile=/var/log/supervisor/%(program_name)s.log
autorestart=false
startsecs=0
[program:nginx]
priority=10
command=nginx -g "daemon off;"
stdout_logfile=/var/log/supervisor/nginx.log
stderr_logfile=/var/log/supervisor/nginx.log
autorestart=true
Then you can have as many other processes as you want and supervisor will handle the restarting of them if needed.
That way you could use supervisord in cases where you might need nginx and php5-fpm and it doesn't make much sense to have them apart.
Motivation:
There is nothing wrong in running multiple processes inside of a docker container. If one likes to use docker as a light weight VM - so be it. Others like to split their applications into micro services. Me thinks: A LAMP stack in one container? Just great.
The answer:
Stick with a good base image like the phusion base image. There may be others. Please comment.
And this is yet just another plead for supervisor. Because the phusion base image is providing supervisor besides of some other things like cron and locale setup. Stuff you like to have setup when running such a light weight VM. For what it's worth it also provides ssh connections into the container.
The phusion image itself will just start and keep running if you issue this basic docker run statement:
moin#stretchDEV:~$ docker run -d phusion/baseimage
521e8a12f6ff844fb142d0e2587ed33cdc82b70aa64cce07ed6c0226d857b367
moin#stretchDEV:~$ docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS
521e8a12f6ff phusion/baseimage "/sbin/my_init" 12 seconds ago Up 11 seconds
Or dead simple:
If a base image is not for you... For the quick CMD to keep it running I would suppose something like this for bash:
CMD exec /bin/bash -c "trap : TERM INT; sleep infinity & wait"
Or this for busybox:
CMD exec /bin/sh -c "trap : TERM INT; (while true; do sleep 1000; done) & wait"
This is nice, because it will exit immediately on a docker stop.
Just plain sleep or cat will take a few seconds before the container is forcefully killed by docker.
Updates
As response to Charles Desbiens concerning running multiple processes in one container:
This is an opinion. And the docs are pointing in this direction. A quote: "It’s ok to have multiple processes, but to get the most benefit out of Docker, avoid one container being responsible for multiple aspects of your overall application." For sure it obviously much more powerful to devide your complex service into multiple containers. But there are situations where it can be beneficial to go the one container route. Especially for appliances. The GitLab Docker image is my favourite example of a multi process container. It makes deployment of this complex system easy. There is no way for mis-configuration. GitLab retains all control over their appliance. Win-Win.
Make sure that you add daemon off; to you nginx.conf or run it with CMD ["nginx", "-g", "daemon off;"] as per the official nginx image
Then use the following to run both supervisor as service and nginx as foreground process that will prevent the container from exiting
service supervisor start && nginx
In some cases you will need to have more than one process in your container, so forcing the container to have exactly one process won't work and can create more problems in deployment.
So you need to understand the trade-offs and make your decision accordingly.
Since docker engine v1.25 there is an option called init.
Docker-compose included this command as of version 3.7.
So my current CMD when running a container that should run into infinity:
CMD ["sleep", "infinity"]
and then run it using:
docker build
docker run --rm --init app
crf.:
rm docs and init docs
Capture the PID of the ngnix process in a variable (for example $NGNIX_PID) and at the end of the entrypoint file do
wait $NGNIX_PID
In that way, your container should run until ngnix is alive, when ngnix stops, the container stops as well
Along with having something along the lines of : ENTRYPOINT ["tail", "-f", "/dev/null"] in your docker file, you should also run the docker container with -td option. This is particularly useful when the container runs on a remote m/c. Think of it more like you have ssh'ed into a remote m/c having the image and started the container. In this case, when you exit the ssh session, the container will get killed unless it's started with -td option. Sample command for running your image would be: docker run -td <any other additional options> <image name>
This holds good for docker version 20.10.2
There are some cases during development when there is no service yet but you want to simulate it and keep the container alive.
It is very easy to write a bash placeholder that simulates a running service:
while true; do
sleep 100
done
You replace this by something more serious as the development progress.
How about using the supervise form of service if available?
service YOUR_SERVICE supervise
Once supervise is successfully running, it will not exit unless it is
killed or specifically asked to exit.
Saves having to create a supervisord.conf
I have been running docker processes (apps) via
docker run …
But under runit supervision (runit is like daemontools) - so runit ensures that the process stays up, passes signals etc.
Is this reasonable? Docker seems to want to run its own demonization - but it isn't as thorough as runit. Furthermore, when runit restarts the app - a new container is created each time (fine) but it leaves a trace of the old one around - this seems to imply I am doing it in the wrong way.
Should docker not be run this way?
Should I instead set up a container from the image, just once, and then have runit run/supervise that container for all time?
Docker does do some management of daemonized containers: if the system shuts down, then when the Docker daemon starts it will also restart any containers that were running at the time the system shut down. But if the container exits on its own or the kernel (or a user) kills the container while it is running, the Docker daemon won't restart it. In cases where you do want a restart, a process manager makes sense.
I don't know runit so I can't give specific configuration guidance. But you should probably make the process manager communicate with the docker daemon and check to see if a given container id is running (docker ps | grep container_id or equivalent, or use the Docker Remote API directly). If the container has stopped, use Docker to restart it (docker run container_id) instead of running a new container. Or, if you do want a new container each time, then begin with docker run -rm to automatically clean it up when it exits or stops.
If you don't want your process manager to poll docker, you could instead run something that watches docker events.
You can get the container_id when you start the container as the return value of starting a daemon, or you can ask Docker to write this out to a file (docker run -cidfile myfilename, like a PID file)
I hope that helps or helps another runit guru offer more detailed advice.
Yes, I think running docker under runit makes sense. Typically when you start a process there is a way to tell it not to daemonize if it does by default since the normal way to hand-off from the runit run script to a process is via exec on the last line of your run script. For docker this means making sure not to set the -d flag.
For example, with docker you probably want your run script to look something like this:
#!/bin/bash -e
exec 2>&1
exec chpst -u dockeruser docker run -a stdin -a stdout -i ...
Using exec and chpst should resolve most issues with processes not terminating correctly when you bring down a runit service.