How to Edit a File After You Shell to a Docker Container

TLDR

To edit a file inside a running Docker container, shell in with docker exec -it <container> sh or bash, then use a text editor like vi or nano. For persistent changes, update your Docker image or use volumes.

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Sometimes you need to make a quick change inside a running Docker container - maybe to debug, patch a config, or test a fix. Docker makes it easy to get a shell inside your container, but there are a few things to keep in mind.

Getting a Shell Inside the Container

First, find your container's name or ID:

docker ps

Then shell in:

# Use sh (for Alpine or minimal images)
docker exec -it <container_name_or_id> sh

# Or bash (for Ubuntu/Debian-based images)
docker exec -it <container_name_or_id> bash

Now you're inside the container and can navigate the filesystem.

Editing Files with Built-in Editors

Most containers include vi or vim. Some minimal images (like Alpine) may only have vi or no editor at all. Try:

vi /path/to/file

If you prefer nano and it's not installed, you can add it (if the container has a package manager):

# For Alpine
apk add nano

# For Debian/Ubuntu
apt-get update && apt-get install nano

Then edit your file:

nano /path/to/file

Making Changes Persistent

Edits made inside a running container are lost if the container is deleted. For changes you want to keep:

• Update your Dockerfile and rebuild the image.
• Use Docker volumes to mount files from your host.
• Commit changes to a new image (not recommended for production):

docker commit <container_name_or_id> my-edited-image:latest

This creates a new image with your changes, but it's better to update the Dockerfile for reproducibility.

Best Practices

• Use shell edits for debugging, not for production changes.
• Always document any manual changes.
• Prefer updating your Dockerfile for reproducibility.

With these steps, you can quickly edit files inside containers and understand how to make those changes stick.

Good luck with your project!