docker run basics

Learn the basic use of the docker run command.

docker run basics

It has the form docker run [options] image [command]. A command written after the image replaces the image's default start command:

docker run ubuntu echo "Merhaba"     # echo runs, the container stops
docker run ubuntu cat /etc/os-release # prints the Ubuntu version info

A container stops the moment its main process (here echo) ends. That is why long-running processes like a web server keep the container open, while one-off commands close immediately.

The image tag

An image name has the form name:tag. If no tag is given, latest is used; but latest doesn't mean "newest", it's just the default tag. For reproducibility the version should always be written:

docker run ubuntu:24.04 cat /etc/os-release
docker run python:3.12-slim python --version   # Python 3.12.x

Exercise Passing a command

Write the command that runs python --version in the python:3.12-slim image and deletes the container when done.

Test yourself

What is the container's state after docker run ubuntu echo merhaba?
- Paused
- Stopped (Exited), because the main process ended
- Running
- Removed
Show answer

Stopped (Exited), because the main process ended — A container's lifetime is tied to its main process.

Use a specific Ubuntu version.

docker run ubuntu____ cat /etc/os-release

Show answer

docker run ubuntu:24.04 cat /etc/os-release

Match.

ubuntu

ubuntu:latest
echo merhaba

Replaces the default command
Exited

Main process ended
python:3.12-slim

Versioned tag

Next lesson: Running in the background

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