How can I run a docker exec command inside a docker container

Question

When I try to run the following command I get an error :

docker exec -i nullmailer sendmail -f user@yahoo.com

This shows the following error:

the docker command does not exist

Comments

After download virtualbox i will Click on virtualbox it is asking 32-bit windows hosts are not supported by this virtualbox release please tall me fast bro

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Hi@Prasad,

You need to enable Virtualization in your windows system. Go to your BIOS and enable it. It will work.

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1. Use docker ps to get the name of the existing container.
2. Use the command docker exec -it <container name> /bin/bash to get a bash shell in the container.
3. Or directly use docker exec -it <container name> <command> to execute whatever command you specify in the container.

May be this can help. I am new here and found this. 

Answer 1

you can run any command in a running container just knowing its ID (or name):

docker exec -it <container_id_or_name> echo "I'm inside the container!"

Note:The container needs to be running.

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Comments

If you’re walking the boxes on the equal host then you may execute docker commands in the field. This can be executed by way of defining the Mailinator for using temp emails docker socket inside the container.

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are you sure about it?

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Did you try this?

Answer 2

If you’re running the containers on the same host then you can execute docker commands within the container. This can be done by defining the docker socket in the container.

To do this, run the container and mount the 'docker.sock' in the following manner:

docker run -v /var/run/docker.sock:/var/run/docker.sock ...

You can finally execute docker commands from inside the container.

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Answer 3

You need to get inside the container and then try to execute your command

Follow these steps:

• Use docker ps to get the name of the existing container
• Use the command docker exec -it <container name> /bin/bash to get a bash shell in the container
• Or directly use docker exec -it <container name> <command> to execute whatever command you specify in the container.

Answer 4

Run the container in the following manner:

docker run -it -d ashok/pyashokproj bin/bash

If you would like to attach to an already running container:

docker exec -it CONTAINER_ID /bin/bash

Answer 5

This seemed pretty simple and helped me.

• To start an existing container which is stopped

docker start <container-name/ID>

• To stop a running container

docker stop <container-name/ID>

• Then to login to the interactive shell of a container

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

Answer 6

This shouldhelp

docker create --name=new_container -it ubuntu
docker start new_container
// ps -a says 'Up X seconds'
docker exec new_container /path/to/my/command
// ps -a still says 'Up X+Y seconds'
docker exec new_container /path/to/another/command

Answer 7

To make debugging easier, we’re introducing docker exec, which allows a user to spawn a process inside their Docker container via the Docker API and CLI.  For example…

$ docker exec -it ubuntu_bash bash

will create a new Bash session inside the container ubuntu_bash.

Answer 8

You can run a command in a container:

 docker-compose run <container name> <command>

 For example, to get a shell into your web container you might run 

docker-compose run web /bin/bash

To run a series of commands, you must wrap them in a single command using a shell. For example:

docker-compose run <name in yml> sh -c '<command 1> && <command 2> && <command 3>'

Answer 9

Use bash with -c

docker exec -it CONTAINER_ID bash -c "mydocker_sql /usr/share/zoneinfo | mysql mysql"

Answer 10

Another approach is to start and attach the container at the same time. Something like this:

docker start <CONTAINER_ID/CONTAINER_NAME> && docker attach <CONTAINER_ID/CONTAINER_NAME> 

Answer 11

I guess there’s no docker runtime in your container.

I am not sure if this will work. Run the container interacitvely and install docker there. Docker can run on a host or virtual machine, I guess not be able to run at a container

Comments

What do you mean by "Run the container interactively"?

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He's trying to say, get into the "interactive mode" with docker container. use the docker run command with this flag: 

docker run -it

Answer 12

Hi,

The command to execute something in a container is - 

docker exec <container_id/container_name> <instruction/cmd to be executed>

In your case, you are trying to send a mail I believe, so:

docker exec -d <container_name> sendmail -f user@yahoo.com

This should run the command in a detached state/ run the process in the background.

In case you want your stdin to be open, replace -d with -i.

sendmail is an utility I believe, incase it is not running, run the command from inside the container and if needed install the sendmail util:

docker exec -i -t <container_name> /bin/bash (or /bin/sh)

This tells docker to run it in an interactive mode, gives you back a tty/terminal and runs the /bin/bash command to provides you a bash terminal basically.

Run the cmd from the terminal and check :)

Also check the root process inside the container : PID 1
The command started using docker exec only runs while the container’s primary process (PID 1) is running, and it is not restarted if the container is restarted.

ref : https://docs.docker.com/engine/reference/commandline/exec/

Comments

Hi Priyak. Thanks for such an amazing explanation. I have a doubt though. What do you mean by 

"If you want your stdin to be open"

Answer 13

If you want to run or execute commands from one container to another you can to ssh but there is another way to do it.

first, you need to go to your host os and edit the docker.service file to enable TCP requests with docker. with this, any os in your network can access your docker commands (even other containers connected to host).

check the below link where I have enabled docker commands to run from container to host. I have also shared the dockerfile for your reference.

https://hub.docker.com/r/smc181002/docker_enabled

Answer 14

this is informative

Answer 15

docker exec -it <container name> bash

Answer 16

You can follow these steps:

1. Use docker ps to get the name of the existing container.
2. Use the command docker exec -it <container name> /bin/bash to get a bash shell in the container.
3. Or directly use docker exec -it <container name> <command> to execute whatever command you specify in the container.

Hope this will help

Best Regards

Answer 17

docker exec -it <container_id_or_name> echo "I'm inside the container!"

Run with different codes if its not working

Answer 18

You can run the below command.

$ docker ps --all

Get the image you want to execute commands in and run:

$ docker run -it --entrypoint /bin/bash $IMAGE_NAME -s

Answer 19

Hi,

You can execute a command on the container using the docker exec command.

$ docker exec -d ubuntu_bash touch /tmp/execWorks

This will create a new file /tmp/execWorks inside the running container ubuntu_bash, in the background. Next, execute an interactive bash shell on the container.

$ docker exec -it ubuntu_bash bash