How to Start a Container in Docker: Simple Commands and Examples

To start a container in Docker, use docker run to create and start a new container from an image, or use docker start to start an existing stopped container. The docker run command combines creation and starting, while docker start only starts containers that already exist.

Syntax

The main commands to start containers in Docker are:

• docker run [OPTIONS] IMAGE [COMMAND] [ARG...]: Creates and starts a new container from the specified image.
• docker start [OPTIONS] CONTAINER: Starts an existing stopped container by its name or ID.

Options can customize container behavior, like -d to run in background (detached mode) or -p to map ports.

bash

docker run [OPTIONS] IMAGE [COMMAND] [ARG...]
docker start [OPTIONS] CONTAINER

Example

This example shows how to start a new container running the nginx web server in detached mode and then start a stopped container.

bash

# Start a new nginx container in detached mode
$ docker run -d --name mynginx -p 8080:80 nginx

# Stop the container
$ docker stop mynginx

# Start the stopped container again
$ docker start mynginx

Output

a1b2c3d4e5f6g7h8i9j0k1l2m3n4o5p6q7r8s9t0u1v2w3x4y5z6
mynginx

Common Pitfalls

Common mistakes when starting containers include:

• Using docker start on a container that does not exist or is already running.
• Forgetting to map ports with -p when running services that need network access.
• Not using -d to run containers in the background, causing the terminal to be blocked.

Example of wrong and right usage:

bash

# Wrong: Trying to start a container that does not exist
$ docker start unknown_container
Error: No such container: unknown_container

# Right: Run a new container first
$ docker run -d --name known_container nginx

# Then start it if stopped
$ docker start known_container

Output

Error: No such container: unknown_container

<container_id>
known_container

Quick Reference

Command	Description	Example
docker run	Create and start a new container	docker run -d -p 80:80 nginx
docker start	Start an existing stopped container	docker start mycontainer
docker stop	Stop a running container	docker stop mycontainer
docker ps	List running containers	docker ps
docker ps -a	List all containers	docker ps -a

Key Takeaways

Use docker run to create and start a new container from an image.

Use docker start to start a container that was previously stopped.

Remember to map ports with -p if your container needs network access.

Use -d option to run containers in the background.

Check container status with docker ps before starting or stopping.