Working with Containers
Containers are instances of Docker images that can be run using the Docker run command. The basic purpose of Docker is to run containers. Let’s discuss how to work with containers.
Running a Container
Running of containers is managed with the Docker run command. To run a container in an interactive mode, first launch the Docker container.
sudo docker run –it centos /bin/bash
Then hit Crtl+p and you will return to your OS shell.
You will then be running in the instance of the CentOS system on the Ubuntu server.
Listing of Containers
One can list all of the containers on the machine via the docker ps command. This command is used to return the currently running containers.
docker ps
Syntax
docker ps
Options
None
Return Value
The output will show the currently running containers.
Example
sudo docker ps
Let’s see some more variations of the docker ps command.
docker ps -a
This command is used to list all of the containers on the system
Syntax
docker ps -a
Options
- ─a − It tells the docker ps command to list all of the containers on the system.
Return Value
The output will show all containers.
Example
sudo docker ps -a
docker history
With this command, you can see all the commands that were run with an image via a container.
Syntax
docker history ImageID
Options
- ImageID − This is the Image ID for which you want to see all the commands that were run against it.
Return Value
The output will show all the commands run against that image.
Example
sudo docker history centos
The above command will show all the commands that were run against the centos image.
Docker top
With this command, you can see the top processes within a container.
Syntax
docker top ContainerID
Options
- ContainerID − This is the Container ID for which you want to see the top processes.
Return Value
The output will show the top-level processes within a container.
Example
sudo docker top 9f215ed0b0d3
The above command will show the top-level processes within a container.
docker stop
This command is used to stop a running container.
Syntax
docker stop ContainerID
Options
- ContainerID − This is the Container ID which needs to be stopped.
Return Value
The output will give the ID of the stopped container.
Example
sudo docker stop 9f215ed0b0d3
The above command will stop the Docker container 9f215ed0b0d3.
docker rm
This command is used to delete a container.
Syntax
docker rm ContainerID
Options
- ContainerID − This is the Container ID which needs to be removed.
Return Value
The output will give the ID of the removed container.
Example
sudo docker rm 9f215ed0b0d3
The above command will remove the Docker container 9f215ed0b0d3.
docker stats
This command is used to provide the statistics of a running container.
Syntax
docker stats ContainerID
Options
- ContainerID − This is the Container ID for which the stats need to be provided.
Return Value
The output will show the CPU and Memory utilization of the Container.
Example
sudo docker stats 9f215ed0b0d3
The above command will provide CPU and memory utilization of the Container 9f215ed0b0d3.
docker attach
This command is used to attach to a running container.
Syntax
docker attach ContainerID
Options
- ContainerID − This is the Container ID to which you need to attach.
Return Value
None
Example
sudo docker attach 07b0b6f434fe
The above command will attach to the Docker container 07b0b6f434fe.
docker pause
This command is used to pause the processes in a running container.
Syntax
docker pause ContainerID
Options
- ContainerID − This is the Container ID to which you need to pause the processes in the container.
Return Value
The ContainerID of the paused container.
Example
sudo docker pause 07b0b6f434fe
The above command will pause the processes in a running container 07b0b6f434fe.
docker unpause
This command is used to unpause the processes in a running container.
Syntax
docker unpause ContainerID
Options
- ContainerID − This is the Container ID to which you need to unpause the processes in the container.
Return Value
The ContainerID of the running container.
Example
sudo docker unpause 07b0b6f434fe
The above command will unpause the processes in a running container: 07b0b6f434fe
docker kill
This command is used to kill the processes in a running container.
Syntax
docker kill ContainerID
Options
- ContainerID − This is the Container ID to which you need to kill the processes in the container.
Return Value
The ContainerID of the running container.
Example
sudo docker kill 07b0b6f434fe
The above command will kill the processes in the running container 07b0b6f434fe.
Docker – Container Lifecycle
The following illustration explains the entire lifecycle of a Docker container.
- Initially, the Docker container will be in the created state.
- Then the Docker container goes into the running state when the Docker run command is used.
- The Docker kill command is used to kill an existing Docker container.
- The Docker pause command is used to pause an existing Docker container.
- The Docker stop command is used to pause an existing Docker container.
- The Docker run command is used to put a container back from a stopped state to a running state.
