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The -v flag

Learn to mount volumes with the -v flag.

-v and --mount

There are two ways to write a volume mount. -v is short: source:target[:option]. --mount uses key=value form; it's longer but readable and reports errors more clearly:

docker run -d -v pgdata:/var/lib/postgresql/data postgres:16
docker run -d --mount type=volume,source=pgdata,target=/var/lib/postgresql/data postgres:16

Both give the same result.

Seeing the mounts

docker inspect shows a container's mounts with their types, sources and destinations:

$ docker inspect -f '{{range .Mounts}}{{.Type}} {{.Name}} -> {{.Destination}}{{"\n"}}{{end}}' db
volume pgdata -> /var/lib/postgresql/data

Practice Mount with --mount

Start a container named cache from redis:7 in the background; mount the redisdata volume at /data with --mount.

Starter code

terminal
# buraya yaz

Expected output

5e6f708192a3

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 In a bind mount, if the host folder doesn't exist, what is the difference between -v and --mount?

  • -v silently creates the folder; --mount errors Correct answer
  • Both error
  • Both create it
  • --mount creates it; -v errors

Explanation: A mistyped path can silently become an empty folder with -v.

2 Give the target directory with --mount.

Question 
docker run -d --mount type=volume,source=pgdata,____=/var/lib/postgresql/data postgres:16
Answer 
docker run -d --mount type=volume,source=pgdata,target=/var/lib/postgresql/data postgres:16

Explanation: target (or destination/dst) is the container path.

3 Match.

Term Meaning
-v Short form
--mount Key=value form
type=volume Volume type
readonly Read-only in --mount

All lessons in Beginner

1 What is Docker?

  1. What is Docker?
  2. Containers and virtual machines
  3. Images and containers
  4. Docker architecture
  5. Use cases
  6. Summary - What is Docker

2 Installation and first commands

  1. Installing Docker
  2. docker version
  3. docker info
  4. The hello-world container
  5. Docker Desktop
  6. Summary - Installation

3 First container

  1. docker run basics
  2. Running in the background
  3. docker ps
  4. docker stop and rm
  5. docker logs
  6. Summary - First container

4 Dockerfile basics

  1. What is a Dockerfile?
  2. The FROM instruction
  3. The RUN instruction
  4. COPY and ADD
  5. CMD and ENTRYPOINT
  6. Summary - Dockerfile

5 Build and images

  1. docker build
  2. Tagging images
  3. Build context
  4. Layers and cache
  5. .dockerignore
  6. Summary - Build

6 docker run options

  1. Interactive mode
  2. Naming containers
  3. Restart policy
  4. Working directory
  5. Switching users
  6. Summary - docker run

7 Image management

  1. docker images
  2. docker rmi
  3. docker pull
  4. docker push
  5. docker tag
  6. Summary - Image management

8 Port mapping

  1. The port concept
  2. The -p flag
  3. Multiple ports
  4. Random ports
  5. IP binding
  6. Summary - Port mapping

9 Volumes and data

  1. Data persistence
  2. Named volumes
  3. The -v flag
  4. Bind mounts
  5. Volume management
  6. Summary - Volumes

10 Environment variables

  1. The -e flag
  2. The ENV instruction
  3. The ARG instruction
  4. env-file
  5. The WORKDIR instruction
  6. Summary - Environment

11 Project: docker-compose

  1. Compose design
  2. Service definition
  3. Database service
  4. Volume and network
  5. Putting it together - compose

12 Docker Hub and registry

  1. What is Docker Hub?
  2. docker login
  3. Searching images
  4. Official images
  5. Private registry
  6. Summary - Registry

13 Network basics

  1. Network drivers
  2. docker network ls
  3. Bridge network
  4. Container connectivity
  5. Publishing ports
  6. Summary - Network

14 Beginner final

  1. Challenge - Dockerfile
  2. Challenge - Build and run
  3. Challenge - Volume
  4. Challenge - Compose
  5. Challenge - Beginner project