How to run docker containers in the background of your terminal

When we create a container from an image, by default, it attaches the container to the terminal. Many cases, we do not want that to happen for we have other commands to execute and do not bother to open new terminals. >_O

In that case, running a docker container in detached mode comes handy.

The default attached mode:#

To create and run a container, we use the following command:

$ docker run eclipse-mosquitto
1555249625: mosquitto version 1.5.8 starting
1555249625: Config loaded from /mosquitto/config/mosquitto.conf.
1555249625: Opening ipv4 listen socket on port 1883.
1555249625: Opening ipv6 listen socket on port 1883.

The above command creates a container with generated name and attaches it to you terminal. When we press CTRL + C, it actually stops the container. But, we do not want that!

Detached Mode:#

For that we have an option to be supplied like this:

$ docker run -d eclipse-mosquitto
09bb7465c787fc1ff2f4177a8d0dd1d5c9751b3192583df5c177968dcacb17a2

Now it does the same job and instead of attaching the container to the terminal it only logs the container id.

How do we know that our container was created successfully and running? In short, we do not!

Check/tail the container logs:#

To we the container's logs:

$ docker logs 09bb7465c787fc1ff2f4177a8d0dd1d5c9751b3192583df5c177968dcacb17a2
1555249810: mosquitto version 1.5.8 starting
1555249810: Config loaded from /mosquitto/config/mosquitto.conf.
1555249810: Opening ipv4 listen socket on port 1883.
1555249810: Opening ipv6 listen socket on port 1883.

Use docker ps to list out the running containers, in case you want to know the name of your running containers. It is better to use -a option to list out all the containers. On error cases, the container might not be running.

Bonus: Attaching the container back:#

Just in case if you want to attach a container back again, it is good to know the attach mode.

$ docker attach 09bb7465c787fc1ff2f4177a8d0dd1d5c9751b3192583df5c177968dcacb17a2

Remember that pressing CTRL + C terminates the container.