I succefully ran hello-world using docker run command , but when I check running containers with docker ps , this container was not visble under running containers ,
Any suggestions
Thank
Rajendar
The default hello-world image from docker has no extra service running inside it so therefore exits after printing the default text. As such you cannot view it using docker ps which is command for viewing currently running containers.
To view running/stopped containers, run docker ps -a
See the image on how the docker ps and docker ps -a command show different results for the `hello-world image.
How did you run it? If I remember correctly, the hello world example just echos and quits, so running docker ps immediately afterwards won't show you anything.
Try this instead:
docker ps -n 1
That will essentially show you the most recent container you ran and its state.
Just for fun, if you really want to watch the hello-world execution at runtime...
Open up a new terminal window and run the command docker events, then keep watching what happens when you run docker run hello-world in your original terminal window.
Magically, you will see your entire container life-cycle below:
1.container create (notice the funny name= attribute of your ephemeral container name)
2.image pull
3.container init
4.container start
5.container attach
6.container died
7.container cleanup
Enjoy!
Related
when calling docker ps the list is empty, although I got an id:
(dcbb6aeaa06ba43fcb.....)
My steps:
Step 1: I created an image (imagekommando) of an running js.file:
Step 2: I created a container (in background) based on my image
docker run -d --name containerkommando imagekommando
I got an id! (container-id??)
Step 3: But docker ps shows empty list:
But when I repeat Step 2, I'm told, that the container (containerkommando) already exists:
docker run -d --name containerkommando imagekommando
Could you help me, understanding the logic behind?
And how can I get the container running (by ID)?
That means that the docker container exited with an error but clean up is required. With --rm option you can tell the docker to remove the container when the container has exited.
docker run --rm .....
Also to check the reason for the container exiting...you can use
docker logs <container_id>
What probably takes place here:
docker run ... creates and starts your container
your container exits
docker ps doesn't list stopped containers (default shows just running), so it made you think that it's not there.
docker run ... fails because you are trying to create and run a container with a name that already exists.
Further reading:
What are the possible states for a docker container?
Why docker container exits immediately
In Docker, a container is automatically exited when the task is finished. You have to specify a correct entrypoint to keep your docker container up.
You can check the exited containers with the command docker ps -a. This exited container will prevent you from using the name again.
So, you may want to use docker rm <container-name> before creating your new container. In a test environement, you can also use docker system prune to clean all unused container/networks.
docker ps only shows the active containers (the running ones).
Your container most probably exited right after you started it. You can use the container ID and do docker logs <container-id> to examine the reason why the container failed.
If you want to see the stopped containers together with the running containers you can do docker ps -a to get a list of all these.
Execute
docker logs <CONTAINER ID>
to view the logs of docker container run.
I faced a similar issue found out there was space issue win my docker. After clearing space the container was able to run.
I'm new to docker.
I have an image that I want to run, but I want docker to see if that image is already running from another terminal...if it is running I don't want it to load another one...
is this something that can be done with docker?
if it helps, I'm running the docker with a privileged mode.
I've tried to search for singleton docker or something like that, but no luck.
updates-
1.working from ubuntu.
My scenario- from terminal X I run docker run Image_a
from terminal Y I run docker run Image_a
when trying to run from terminal Y, I want docker to check if there is already a docker running with Image_a, and the answer is true - I want docker not to run in terminal Y
You can use the following docker command to get all containers that running from specific image:
docker ps --filter ancestor="imagename:tag"
Example:
docker ps --filter ancestor="drone/drone:0.5"
Example Output:
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
3fb00087d4c1 drone/drone:0.5 "/drone agent" 6 days ago Up 26 minutes 8000/tcp drone_drone-agent_1
This approach uses docker api and docker daemon, so it doesnt matter if the run command executed in background or other terminal.
Aother approach:
If you have a single container form a single image:
Try naming your containers, You cant have 2 containers with the same name:
docker run --name uniquecontainer Image_a
Next time you run the above command you will get an error. Btw consider using -d so you dont have to switch terminals.
docker run -d --name uniquecontainer Image_a
What is the difference between docker run and docker create commands?
I usually use run but sometimes in documentation I see create.
Docker's --help tells
create Create a new container
run Run a command in a new container
Does it mean that run is used when we need to pass a command to a new container? What's the aim of create then?
docker run = docker create + docker start.
From docker documentation
The docker create command creates a writeable container layer over the
specified image and prepares it for running the specified command. The
container ID is then printed to STDOUT. This is similar to docker run
-d except the container is never started. You can then use the docker start command to start the container at any point.
This is useful when you want to set up a container configuration ahead
of time so that it is ready to start when you need it. The initial
status of the new container is created.
docker create command creates a writeable container from the image and prepares it for running.
docker run command creates the container (same as docker create) and starts it.
The other answers have this covered but I thought I'd show the equivalent shell command-lines because it makes it really clear:
$ docker run myimage
is the same as
$ docker start -a $(docker create myimage)
Here, docker create is used to create a container from the named image and outputs the created container id and docker start is used to start the container with that id. The -a option causes the terminal to attach so that the container runs in the foreground which is the default behaviour of docker run.
A container that has been created but never started will have a Created status; this can be seen with docker container ls -a.
I'm new to docker and just got around to playing with it;
My take is that docker run essentially does the following: (in the order of..) docker create, docker start, docker attach , since it immediately attaches to the active shell after you do the 'run' command.
to create a container:
to start a container:
to create and start with a single command:
Now to understand we must dig deep with create and start.
Process of creating a container is taking the file system from image, and kind of prep it for use in the new container. When we create the container we are just prepping or setting up the file system snapshot to be used to create the container to actually start the container.
So creating container is about the file system starting it is about actually executing the startup the command.
And to start the container, we actually execute the start up command that might start up the process.
Lets see it in terminal:
When I run command "sudo docker create hello-world" it prints bellow output.
In the output we saw characters printed out. This is the ID of the container that was just created, Now I can actually execute the hello world command inside of this container by running Docker start.
So what happened here, first off we kind of prop the container by getting the file system ready.
Then after that we actually executed the primary start up command in there with Docker start.
-a in the docker start command is for watching output from the container and print it out to your terminal.
So there is very small difference between Docker run and docker start, by default Docker run is going to show you all the logs or all the information coming out of the container. By default Docker start is the opposite Docker start is not going to show you information coming out of the terminal.
Now you know when you need to use Run / Create / Start
Docker run is basically for running commands in the container.
docker run -it <Container Name> /bin/bash
The above is for creating a bash terminal. And make us use bash commands in the container.
Docker create is to create a container from an Docker Image.
docker create -d /var/lib:/var/lib --name docker-ubuntu ubuntu
The above is to create a docker a container of the name "docker-ubuntu" from the image "ubuntu"
In practice to start a container I do:
docker run a8asd8f9asdf0
If thats the case, what does:
docker start
do?
In the manual it says
Start one or more stopped containers
This is a very important question and the answer is very simple, but fundamental:
Run: create a new container of an image, and execute the container. You can create N clones of the same image. The command is:
docker run IMAGE_ID and not docker run CONTAINER_ID
Start: Launch a container previously stopped. For example, if you had stopped a database with the command docker stop CONTAINER_ID, you can relaunch the same container with the command docker start CONTAINER_ID, and the data and settings will be the same.
run runs an image
start starts a container.
The docker run doc does mention:
The docker run command first creates a writeable container layer over the specified image, and then starts it using the specified command.
That is, docker run is equivalent to the API /containers/create then /containers/(id)/start.
You do not run an existing container, you docker exec to it (since docker 1.3).
You can restart an exited container.
Explanation with an example:
Consider you have a game (iso) image in your computer.
When you run (mount your image as a virtual drive), a virtual drive is created with all the game contents in the virtual drive and the game installation file is automatically launched. [Running your docker image - creating a container and then starting it.]
But when you stop (similar to docker stop) it, the virtual drive still exists but stopping all the processes. [As the container exists till it is not deleted]
And when you do start (similar to docker start), from the virtual drive the games files start its execution. [starting the existing container]
In this example - The game image is your Docker image and virtual drive is your container.
run command creates a container from the image and then starts the root process on this container. Running it with run --rm flag would save you the trouble of removing the useless dead container afterward and would allow you to ignore the existence of docker start and docker remove altogether.
run command does a few different things:
docker run --name dname image_name bash -c "whoami"
Creates a Container from the image. At this point container would have an id, might have a name if one is given, will show up in docker ps
Starts/executes the root process of the container. In the code above that would execute bash -c "whoami". If one runs docker run --name dname image_name without a command to execute container would go into stopped state immediately.
Once the root process is finished, the container is stopped. At this point, it is pretty much useless. One can not execute anything anymore or resurrect the container. There are basically 2 ways out of stopped state: remove the container or create a checkpoint (i.e. an image) out of stopped container to run something else. One has to run docker remove before launching container under the same name.
How to remove container once it is stopped automatically? Add an --rm flag to run command:
docker run --rm --name dname image_name bash -c "whoami"
How to execute multiple commands in a single container? By preventing that root process from dying. This can be done by running some useless command at start with --detached flag and then using "execute" to run actual commands:
docker run --rm -d --name dname image_name tail -f /dev/null
docker exec dname bash -c "whoami"
docker exec dname bash -c "echo 'Nnice'"
Why do we need docker stop then? To stop this lingering container that we launched in the previous snippet with the endless command tail -f /dev/null.
daniele3004's answer is already pretty good.
Just a quick and dirty formula for people like me who mixes up run and start from time to time:
docker run [...] = docker pull [...] + docker start [...]
It would have been wiser to name the command "new" instead of "run".
Run creates a container instance of an existing (or downloadable) image and starts it.
The first time I ran my configured image, I passed in a --name option. After running the image, I stopped it. Now, it appears in the docker ps output:
vagrant#precise64:~/docker$ docker ps -a
Since it has a name, how can I restart it? It seems that the docker run command only accepts an imageid (not a containerid). And if run it again, a new container is created (which is not what I want).
To start a stopped container one could issue
docker start {name}