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Contents
  1. Docker tutorial
Getting started
  1. What is Docker
  2. Install Docker
  3. Docker Desktop interface tour
  4. Your first container
  5. Images
  6. Container lifecycle
  7. docker run flags
  8. View logs and debug
Images and Dockerfile
  1. Dockerfile basics
  2. Generate files with docker init
  3. Dockerfile instructions
  4. Build Cache and Optimization
  5. Multi-stage builds
  6. Push to Docker Hub
Data and networking
  1. Volumes and data persistence
  2. Networking and container communication
  3. Environment variables and .env
Docker Compose
  1. Docker Compose Tutorial
  2. compose.yaml syntax
  3. Docker Compose commands
  4. Build a WordPress Site
Real-world examples
  1. Python apps
  2. Node.js apps
  3. Nginx and reverse proxying
  4. MySQL
  5. PostgreSQL
  6. Redis
Operations and advanced topics
  1. Reclaim disk space
  2. Security best practices
  3. Rootless and Podman
  4. Multi-platform images
  5. Build automatically with GitHub Actions
  6. Deploy to a cloud server
  7. Internals
  8. Common error messages
  9. Docker command cheat sheet
Command reference
  1. docker build
  2. docker exec
  3. docker ps
  4. docker logs
  5. docker cp
  6. docker inspect
  7. docker volume
  8. docker network
  9. docker compose up
  10. docker compose down

Docker exec tutorial: Run commands in a running container

docker exec runs a command in a running container. It's most often used to enter a container and investigate a problem. For the full debugging workflow, see View logs and debug.

Syntax

docker exec [OPTIONS] CONTAINER COMMAND [ARG...]
docker exec -it web sh        # Enter the container's shell
docker exec web nginx -t      # Run a command and get its output

Options

docker exec doesn't have many options. Here are all the options listed by docker exec --help:

OptionDescription
-i, --interactiveKeep standard input open so you can enter input
-t, --ttyAllocate a terminal. Use with -i for interactive sessions: -it
-u, --user USER[:GROUP]Run as the specified user (name or UID)
-w, --workdir PATHRun in the specified directory inside the container
-e, --env NAME=VALUESet an environment variable for this command
--env-file FILERead environment variables from a file
-d, --detachRun in the background and return immediately
--privilegedGive this command extra privileges (for debugging; don't use it routinely)
--detach-keysChange the key sequence for detaching (default: Ctrl+P, Ctrl+Q)

The examples below all run against an nginx container named web, which was started with the environment variable APP_MODE=demo:

docker run -d --name web -e APP_MODE=demo nginx:1.30-alpine

Run a command

$ docker exec web nginx -v
nginx version: nginx/1.30.5

$ docker exec web sh -c "ls /etc/nginx/conf.d && echo \$APP_MODE"
default.conf
demo
  • The first command runs nginx -v in the container and prints the result directly.
  • To use &&, pipes, or variables, pass the command to the container's shell with sh -c "...". The \ in \$APP_MODE prevents the host shell from expanding the variable first; demo is the value inside the container.

Enter a container interactively

docker exec -it web sh

After you enter, the prompt changes to / #. You can work as you would in a regular Linux environment. Enter exit to leave; the container keeps running. If the image includes bash, you can use bash instead.

-u, -w, and -e

$ docker exec -u nginx web id
uid=101(nginx) gid=101(nginx) groups=101(nginx)

$ docker exec -w /usr/share/nginx/html web ls
50x.html
index.html

$ docker exec -e GREETING=hi web sh -c "echo \$GREETING"
hi
  • -u nginx: Run as the nginx user (the container defaults to root). This is useful for checking file permission problems.
  • -w /usr/share/nginx/html: Run in the specified directory, as if you had run cd first.
  • -e GREETING=hi: Set an environment variable for this command only. It doesn't change the container itself.

-d: Run in the background

$ docker exec -d web sh -c "sleep 2; touch /tmp/done"

$ docker exec web ls /tmp
done

-d runs the command in the background and returns immediately. Check after 2 seconds, and /tmp/done has been created. This is useful for starting work when you don't need to wait for the result.

The container isn't running

$ docker stop web
web

$ docker exec web ls
Error response from daemon: container 1ec4fdc5c592b09b64e8f28869c37f89ab17163f88bfcb09e82815a44b0e1164 is not running

docker exec only works with a running container. Start a stopped container with docker start. If the container exits as soon as it starts, you can't use exec to enter it. Check docker logs instead, or start a new container for inspection with docker run --rm -it --entrypoint sh IMAGE.

Exercises

Exercise: Use one command to list the files in /etc/nginx in the web container as the nginx user.

Answer 
docker exec -u nginx -w /etc/nginx web ls

FAQ

What's the difference between docker exec and docker run?

docker run uses an image to **create a new container**; docker exec runs another process in a **container that's already running**. When exec finishes, it doesn't affect the container itself.

Why does docker exec -it container bash return executable file not found?

The container doesn't have bash. For example, Alpine-based images only include sh. Use docker exec -it container sh instead.

Do files I modify in a container remain after I rebuild the container?

No. Changes made with exec are in the container's writable layer, and disappear when you delete the container. Put changes you need to keep in a Dockerfile or in a Volume.

Updated October 14, 2026