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
Related
I ran a docker container on one of the terminals, on the other terminal:
$ docker container ls
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
80b6be3a7d56 rbonghi/isaac-ros-tutorial:realsense-camera "/ros_entrypoint.sh …" 9 seconds ago Up 8 seconds inspiring_almeida
and then I run
$ docker attach inspiring_almeida
now nothing seems to happen, cursor moves to a new line.
$ docker attach inspiring_almeida
What am I doing wrong? I expected to see something like root#80b6be3a7d56
P.s. I'm accessing the machine that I run docker via SSH - if that matters.
Run docker exec -it inspiring_almeida /bin/bash. It runs a shell inside the container.
attach just connects your input/output terminal with the container's input/output.
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!
I'm using Docker for Windows (Education Edition with Hyper-V) and am fairly new to Docker. My workflow feels a little bit complicated and I think there are better ways. Here's what I do:
When I develop with Docker containers, I add a Dockerfile to my project first.
Then I am going to build the container by running a command like docker build -t containername .
When Docker is done building, I am going to run the container with a command like docker run -p 8080:8080 containername (sometimes I add a volume at this point)
This runs the container and leaves my Powershell in a state where I can read debug messages and so on from the container.
Then I'm testing and developing the application.
Once I'm done developing and testing, I need to CTRL + C in order to exit the running container.
Now comes the tricky part: Say, I forgot something and want to test what I forgot to test right away. I would again run docker build -t containername . BUT docker would now tell me, that the port is already taken. So I continue like this:
I search for my container with this command: docker ps
Once I found the name (i.e. silly_walrusbeard) I type docker stop silly_walrusbeard. Now I can run docker build -t containername . again and the port is now free.
How could I simplify this workflow? Is there an alternative to CTRL+C that also stops the container? Thanks for your suggestions!
list all current containers with docker ps -a. Kill them with docker kill <ID> and maybe docker rm <ID>.
And when you run new containers use the --rm to free ports (among other things) automatically when the container stops:
docker run --rm -it containername
(I usually need the -it when running shells, but I'm not sure about powershell. Maybe you don't need it)
This question already has answers here:
How to continue a Docker container which has exited
(14 answers)
Closed 6 years ago.
A related question & answer on How to start a docker container (ubuntu image) suggest using docker run -it ubuntu to start a ubuntu container and connect to it. However the run command creates and starts a new ubuntu container.
How do we start an existing docker container (ubuntu image) given it's CONTAINER_ID without creating a new container?
Example:
docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
9f297d02f419 ubuntu "/bin/bash" 3 seconds ago Exited (0) 1 seconds ago cranky_wilson
How do we start 9f297d02f419 ?
you can start the stopped container using docker start command -
eg:
docker start 9f297d02f419
If you just use run on the Ubuntu image it will start a container that's running no command, which will immediately stop. You can docker start it but it will stop again. You can see it with docker ps -a.
The accepted answer in that question is very old and not very good. If you run that command on the current Docker version you get an error No command specified!
What you need to do is tell that container to run a command:
docker run ubuntu date
Will run a container from the image, run the date command, then exit. If you want to keep it running indefinitely, try something like:
docker run -d ubuntu tail -f /dev/null
You should see that the container is now running. The -d makes it run in the background, otherwise it will occupy your shell. And the final piece of the puzzle: since we have a container now that's configured to run a command, you can use docker ps to find its ID, and you can docker stop and docker start it at will.
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.