docker exec: Run Commands Inside a Container (with Examples)

Quick Answer

# Enter a running container with bash
docker exec -it CONTAINER_NAME bash

# Enter with sh (Alpine images without bash)
docker exec -it CONTAINER_NAME sh

# Run a single command without entering
docker exec CONTAINER_NAME cat /etc/nginx/nginx.conf

Get your container name from docker ps.

Basic docker exec Syntax

docker exec [OPTIONS] CONTAINER COMMAND [ARG...]

Option	Description
`-i`	Keep stdin open (interactive)
`-t`	Allocate a pseudo-TTY (terminal)
`-u`	Run as a specific user
`-e`	Set an environment variable
`-w`	Set the working directory

Always combine -i and -t as -it when opening an interactive shell. Without -t, you get no prompt. Without -i, input is immediately closed.

Enter a Container Shell

bash (default for most images)

docker exec -it my-nginx bash

sh (Alpine-based images)

Alpine images don’t ship with bash. Use sh:

docker exec -it my-alpine sh

Enter as root for debugging

docker exec -it -u root my-container bash

Enter as a specific user

docker exec -it -u www-data my-container bash

Run a Single Command

# Read a config file
docker exec my-nginx cat /etc/nginx/nginx.conf

# List files
docker exec my-app ls -la /var/log/

# Check environment variables
docker exec my-app env

# Check running processes
docker exec my-app ps aux

Set Environment Variables

# Pass an env var to the command
docker exec -e DEBUG=true my-app node debug.js

# Pass multiple env vars
docker exec -e NODE_ENV=production -e PORT=8080 my-app node app.js

Set Working Directory

docker exec -w /app my-container ls

Using docker exec with docker-compose

Use the service name from docker-compose.yml, not the container name:

# Enter the web service
docker-compose exec web bash

# Connect to PostgreSQL
docker-compose exec db psql -U postgres

# Run a migration
docker-compose exec web rails db:migrate

Check service names with docker-compose ps.

Common Debugging Patterns

Tail a log file live

docker exec my-nginx tail -f /var/log/nginx/error.log

Test network connectivity between containers

docker exec my-app curl -v http://db:5432
docker exec my-app ping redis

Check open ports inside the container

docker exec my-container ss -tlnp

Common Errors

`bash: not found`

The image doesn’t include bash. Use sh:

docker exec -it my-container sh

`the input device is not a TTY`

You’re missing -t. Always use -it for interactive sessions.

`cannot exec in a stopped container`

Start the container first:

docker start CONTAINER_NAME
docker exec -it CONTAINER_NAME bash

docker exec vs docker run

	`docker exec`	`docker run`
Target	Running container	Creates a new container
Use case	Debug live container	Start a fresh container
State	Uses existing state	Starts clean

FAQ

Q: What does docker exec -it mean? -i keeps stdin open, -t allocates a terminal. Together they make the session interactive.

Q: How do I run a command in a Docker container? docker exec CONTAINER_NAME COMMAND. Example: docker exec my-app ls /var/log.

Q: How do I enter a running Docker container? docker exec -it CONTAINER_NAME bash (or sh for Alpine images).

Q: Why does docker exec bash give “bash: not found”? The image is Alpine-based and doesn’t include bash. Use sh instead.

Q: Can I run docker exec on a stopped container? No. Start the container first with docker start CONTAINER_NAME.

Q: What is the difference between docker exec and docker attach? docker exec creates a new process inside the container. docker attach connects to the main process (PID 1). Use exec for debugging.

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