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Specifying user and group in Docker

Kay Gosho on April 24, 2018

If we use Docker as our development environment, we would use docker command to generate files. e.g. docker run --rm ruby:2.4 bundle exec rails...

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Timur Vasyunin • Apr 11 '20

Or you can also set up user/group remapping by configs of your OS (/etc/subuid, /etc/subgid). See docs.docker.com/engine/security/us... to get more information.

It can be more convenient is some cases.

Kay Gosho • May 27 '20

Thanks for the information!

Dev_NIX • Jan 10 '20 • Edited

You can also provide a default value, and override it with the environment variable or with a docker-compose.override.yml:

web:
  build: 
    context: docker/web
    args:
      uuid: ${CURRENT_UID:-1000}

And then in your Dockerfile:

RUN usermod -u $uuid www-data

Kay Gosho • Jan 10 '20

Thank you for the information!

Varun Batra • Sep 21 '18

Any way without export UID?

Kay Gosho • Sep 22 '18

env UID=${UID} GID=${GID} docker-compose up would work without export UID, I suppose!

Varun Batra • Sep 30 '18

Hi, if I do this, on restart (if I have docker always restart) permission is lost on system boot. Hence, this isn't a good way to do it.

Kay Gosho • Oct 16 '18

Hi Varun,

Oh really? I don't have such experiences, as file permission usually doesn't change on system boot.

Varun Batra • Oct 16 '18 • Edited

Let us say that you have a docker container which will keep creating files with some logic - in my case it is compressing the images.

I have written a blog for the docker I have added to a tool:

Lossless Image Compressions using Docker

Now what it does is - it reads image - move image to temp folder, compress it, copy back to its original location.

All goes well as I have started it with $UID as mentioned in your post.

However, let us say now the machine is restarted - somehow $UID becomes a root.

If you have observed the same problem? After restart - some images I uploaded are now compressed with the root user and not www-data as originally intended.