How to execute a command in running Docker container

Sometimes you need to run a particular command on a running container perhaps to check where some files are located or to see their contents, in this quick tips episode, you will learn how. Above is the vid and below you will find some useful notes.

1. 1.

   Pre-reqs

   • Have Docker installed
2. 2.

   Start a Docker container

   • For this video I will be using a Jenkins image as an example, so let’s first download it by using docker pull

     docker pull jenkins/jenkins:lts
     

   • Then I will use one of the suggested ways to run the instance and do it in the background. If you don't use pull first this command will work given that it will also try to download the image if it's not found locally.

     docker run -d -p 8080:8080 -p 50000:50000 jenkins/jenkins:lts
     

   • You can check what's the container id, you can just type docker ps for this

     docker ps
     

   • You can execute a command in a running container with the following:

     docker exec -ti CONTAINER_ID COMAND_TO_RUN
     

     To run bash and do stuff inside the container:

     docker exec -ti CONTAINER_ID  /bin/bash
     

     To print the contents of a file, like the one with the initial password for the jenkins image (/var/jenkins_home/secrets/initialAdminPassword):

     docker exec -ti CONTAINER_ID  cat /var/jenkins_home/secrets/initialAdminPassword
     

     To list files and folders:

     docker exec -ti CONTAINER_ID  ls
     

3. 3.

   Resources

   Jenkins - Docker Hub