Here’s a complete tutorial on the docker cp command, including how it works, its use cases, and a comprehensive list of examples.

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What is docker cp?

docker cp is a Docker command used to copy files or directories between your local machine (host) and a Docker container. It’s similar to the Linux cp command but operates between the host system and Docker containers.

Key Features of docker cp:

• Copy files from the host to a container.
• Copy files from a container to the host.
• Works with absolute and relative paths.
• Supports copying entire directories.

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Basic Syntax

docker cp [OPTIONS] CONTAINER:SRC_PATH DEST_PATH
docker cp [OPTIONS] SRC_PATH CONTAINER:DEST_PATH

Arguments:

• CONTAINER: The name or ID of the container.
• SRC_PATH: The source file or directory path (inside the container or on the host).
• DEST_PATH: The destination file or directory path (inside the container or on the host).

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Examples of docker cp

1. Copy a File from Host to Container

docker cp myfile.txt my_container:/tmp/myfile.txt

This command copies myfile.txt from the host to the /tmp directory of my_container.

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2. Copy a File from Container to Host

docker cp my_container:/etc/hostname ./hostname.txt

This command copies the /etc/hostname file from the container to the current directory on the host and names it hostname.txt.

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3. Copy a Directory from Host to Container

docker cp ./myfolder my_container:/var/myfolder

This copies the entire myfolder directory from the host into /var in the container.

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4. Copy a Directory from Container to Host

docker cp my_container:/usr/share/nginx/html ./nginx-html

This copies the /usr/share/nginx/html directory from the container to the current directory on the host.

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5. Copy a File and Overwrite in the Container

docker cp updated-config.conf my_container:/etc/myapp/config.conf

The existing config.conf in the container is replaced with updated-config.conf from the host.

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6. Copy a File with a New Name

docker cp my_container:/var/log/nginx/access.log ./nginx_access_backup.log

This copies the access.log from the container and saves it on the host as nginx_access_backup.log.

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7. Copy Files Between Two Containers (Indirectly)

Docker does not allow direct copying between containers using docker cp. However, you can do it in two steps:

1. Copy the file to the host: docker cp container1:/path/to/file ./file
2. Copy the file to the second container: docker cp ./file container2:/path/to/file

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8. Using Absolute Paths

docker cp /home/user/myfile.txt my_container:/tmp/

This uses an absolute path to copy myfile.txt from the host to the /tmp directory in the container.

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9. Copying Hidden Files

To copy hidden files (like .env), use:

docker cp ./myfolder/.env my_container:/app/.env

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10. Copy Logs from Container to Host

If you want to copy logs for analysis:

docker cp my_container:/var/log/app.log ./app.log

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11. Copy a File from a Stopped Container

You can still use docker cp on stopped containers:

docker cp stopped_container:/data/backup.tar.gz ./backup.tar.gz

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12. Copy Large Directories

To copy large directories (e.g., database backups or logs), ensure you have enough space on your host:

docker cp my_container:/var/lib/mysql ./mysql_backup

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13. Verify File Copy

After copying, you can verify it with:

docker exec my_container ls -l /path/in/container

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List of Common docker cp Commands

Command	Description
docker cp file.txt my_container:/path/to/file.txt	Copy a file from host to container
docker cp my_container:/path/to/file.txt ./file.txt	Copy a file from container to host
docker cp ./myfolder my_container:/path/in/container	Copy a directory from host to container
docker cp my_container:/path/in/container ./folder	Copy a directory from container to host
docker cp stopped_container:/file ./file	Copy a file from a stopped container to host
docker cp ./file container:/new/path/newfile.txt	Copy a file with a new name in the container
docker cp hidden/.env my_container:/app/.env	Copy hidden files from host to container

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Best Practices

• Use absolute paths for clarity and to avoid mistakes.
• Verify copied files with docker exec or docker logs.
• Avoid overwriting critical files inside the container unless necessary.
• Backup large directories regularly using docker cp to avoid data loss.

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Common Errors and Solutions

1. “No such file or directory”
   → Ensure the file or directory exists on the host or in the container.
2. Permission Denied
   → Check permissions of the destination directory and run Docker commands with the correct privileges (sudo if needed).
3. Container Not Found
   → Ensure the container is running or use the correct name/ID.

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Would you like examples for specific file types, like config files, web assets, or database backups? 😊