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.
Related
I created Dockerfile with the following content,
FROM node:16.4.2-alpine3.14
WORKDIR /app
COPY package.json .
COPY . /app
then I created image,
docker build -t app:0.1 .
and then started the container by running,
docker run -it app:0.1
It opened the node shell.
I then closed it.
Doing docker ps -a gives the following output,
Now,
I want to restart the same container and with node shell. How can it be done?
It shows as exited since there is no process running. To start it again , you can use the docker start command with -i flag.
https://docs.docker.com/engine/reference/commandline/start/ for more options
docker rm the existing container and docker run a new one. Consider using the docker run --rm option so the container deletes itself when it's done.
There's nothing special or valuable about a container; it's just a wrapper around a single process (in your case the Node REPL), and creating a new one isn't especially expensive. In the same way that you can't restart the REPL once you've exited it but need to re-run node, you generally will want to delete and recreate containers once their process has finished. With longer-running processes this also helps ensure the process's filesystem is exactly what you expect: if something exits unexpectedly, deleting the container will also remove any temporary files or lock files it's left behind, so restarting the container will run successfully.
use the following sequence of commands:
docker container start magical_merkle
docker attach magical_merkle
Explanation: the first command restarts your exited container, but in detached mode, it means it's running in the background and you can't see it's output. now for you to reattach to the container you run attach command of docker (second command) which attaches the std io of your host terminal to the std io of the running container.
you may notice the magical_merkle in the commands. this is the name of your container as found in the container ls output you provided. when you run the run command, docker will name the container with a auto generated name if you don't provide one for it.
I'm fairly new to Docker. I have a long Dockerfile that I inherited from a previous developer, which has many errors and I'm trying to get it back to a working point. I commented out most of the file except for just the first line:
FROM ubuntu:14.04
I did the following:
docker build -t pm . to build the image - this works because I can see the image when I execute docker images
docker run <image-id> returns without error or any message. Now I'm expecting the container to be created from the image and started. But when I do a docker ps -a it shows the container exited:
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
b05f9727f516 f216cfb59484 "/bin/bash" About a
minute ago Exited (0) About a minute ago
lucid_shirley
Not sure why can't I get a running container and why does it keep stopping after the docker run command.
executing docker logs <container_id> displays nothing - it just returns without any output.
Your Docker image doesn’t actually do anything, container stop when finish its job. Since here no foreground process running it will start and then immediately stop.
To confirm your container have no issues, try to put below code into a docker-compose.yml(in same folder as the Dockerfile) and run docker-compose up, now you will see your container is running without exiting.
version: '3'
services:
my-service:
build: .
tty: true
Please have a look here Docker official tutorial it will guide you to how to work with docker.
try
docker run -it <image> /bin/bash
to run a shell inside the container.
That won't do much for you, but that'll show you what is happening: as soon as you exit the shell, it will exit the container too.
Your container basically doesn't do anything: it has an image of Ubuntu but doesn't have an ENTRYPOINT or a CMD command to run 'something'
Containers are ephemeral when ran: they run a single command and exit when the command finishes.
Docker container categorized following way.
Task Based : When container start it will start processing and it complete the process then exited.
Background container : It will wait for some request.
As you not provided your docker file so I assume that you have only one statement.
FROM ubuntu:14.04
your build statement create image with name pm.
Now you run
docker run pm
It will start container and stop as you did not provide any entry point.
Now try this
This is one command prompt or terminal.
docker run -it pm /bin/bash
Open another terminal or command prompt.
docker ps ( Now you will see there is one container).
If you want to see container that is continuously running then use following image.
(This is just a example)
docker run -d -p 8099:80 nginx
Above line run one container with Nginx image and when you open your browser http://localhost:8099 you can see the response.
Docker Containers are closely related to the process they are running. This process is specified by the "CMD" part on the Dockerfile. This process has the PID "1". If you kill it, your container is killed. If you haven't one, your container will stop instantly. In your case, you have to "override" your CMD. You can do it with a simple : "docker run -it ubuntu:18.04 bash". "-it" is mandatory since it allows the stdin to be attached to your container.
Have fun with docker.
Each instruction of Dockerfile is a layer within a container which perform some task. In your docker file It's just the loading the ubuntu which is completed when you run the docker within a fraction of seconds and exit since process finished. So if want to have your container running all the time then there should be a foreground process running in your docker.
For testing if you run
docker run <imageid> echo hi it will return the output means your container is fine.
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 am trying to create docker container using dockerfile where script-entry.sh is to be executed when the containers starts and script-exit.sh to be executed when the container stops.
ENTRYPOINT helped to accomplish the first part of the problem where script-entry.sh runs on startup.
How will i make sure the script-exit.sh is executed on docker exit/stop ?
docker stop sends a SIGTERM signal to the main process running inside the Docker container (the entry script). So you need a way to catch the signal and then trigger the exit script.
See This link for explanation on signal trapping and an example (near the end of the page)
Create a script, and save it as a bash file, that contains that following:
$CONTAINER_NAME="someNameHere"
docker exec -it $CONTAINER_NAME bash -c "sh script-exit.sh"
docker stop $CONTAINER_NAME
Run that file instead of running docker stop, and that should do the trick. You can setup an alias for that as well.
As for automating it inside of Docker itself, I've never seen it done before. Good luck figuring it out, if that's the road you want to take.
I'm trying to get a docker container to never shutdown.
If I run a docker container with the -d flag the container will be run in the background.
For example, can this be done:
Start docker container with -it flags
start entrypoint application
entrypoint application creates 10 other services/processes to run in that same container
entrypoint application terminates
Will the docker container stay up now that the application mentioned in the entrypoint has exited?
Why don't you simply try? AFAIU -d or -it won't affect the container termination. And I guess you understand that starting those 10 processes means you violate the docker's idea of one process per container. Why don't you start 10 containers instead? You can also do that from your start container, and they will keep running even if the starting container will terminate.
You could also give docker docs a try: https://docs.docker.com/articles/host_integration/
-it flag means you want your standard input and output routed to/from container. This is basically and conceptually incompatible with running forever.
In general container will shutdown when entry point exits. if you want to keep container running you should run one (probably the last application) not as a background daemon but in foreground. for example if nginx is the last service you want to run. What you would do as your last line of entry point script (if thats a shell script) should be some thing like this:
nginx -g "daemon off;"