Question 81597 in Docker Question posted in
The official documentation can be found here.

What is the meaning of the type/o/device flags in driver_opts in the docker-compose file?

I am working on a project where I have to create costum docker containers with costum volumes etc.
As I have to use some driver_opts, I am wondering, what the flags

type: XXX
o: XXX
device: XXX

in a docker-compose file actually mean. I see all the people using them, but the docker manuals and all the resources I found so far couldn’t provide satisfying answers. I cannot even find a simple list of what arguments you could pass to all theses flags.

thanks in advance!

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2

Answers


  1. 0

    From man mount:

    mount [-fnrsvw] [-t fstype] [-o options] device mountpoint

    To summarize:

    type: AAA
o: BBB
device: CCC

    is (more or less*) equivalent to: mount -t AAA -o BBB CCC <docker_generated_mountpoint>

    * – there is some parsing https://github.com/moby/moby/blob/8d193d81af9cbbe800475d4bb8c529d67a6d8f14/volume/local/local_unix.go#L122

    I cannot even find a simple list of what arguments you could pass to all theses flags.

    This depends on the particular driver you are using. man mount.cifs differs from man mount.nfs, etc.

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  2. 0

    From docker-compose driver_opts:

    driver_opts specifies a list of options as key-value pairs to pass to the driver for this volume. Those options are driver-dependent.

    volumes:
  example:
    driver_opts:
      type: "nfs"
      o: "addr=10.40.0.199,nolock,soft,rw"
      device: ":/docker/example"

    In fact, these opts should exactly same with the one when you use docker run, see Driver-specific options:

    $ docker volume create --driver local 
    --opt type=nfs 
    --opt o=addr=192.168.1.1,rw 
    --opt device=:/path/to/dir 
    foo

    You should in that official document find other opts for other kinds of driver like tmpfs, btrfs etc.

    tmpfs:

    $  docker volume create --driver local 
    --opt type=tmpfs 
    --opt device=tmpfs 
    --opt o=size=100m,uid=1000 
    foo

    btrfs:

     docker volume create --driver local 
    --opt type=btrfs 
    --opt device=/dev/sda2 
    foo

    So, these options is really different depends on the driver type you choose.

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