Mount “named volume” as non-root in Docker

Question

Is there any way to mount a named volume as a non-root user? I am trying to avoid having to run a chown in each Dockerfile but I need the mount to be writable by a non-root user to be able to write the artifacts created by a build in the image

This is what I'm trying

docker run --rm -it -v /home/bob/dev/:/src/dev -v builds:/mnt/build --name build hilikus/build /bin/bash

but for the second mount I get

[user@42f237282128 ~]$ ll /mnt
total 4
drwxr-xr-x 2 root root 4096 Sep 18 19:29 build

My other mount (/src/dev/) is owned by user, not by root so it gives what I need; however, I haven't been able to do the same with the named volume.

Answer 1

The named volume initializes to the contents of your image at that location, so you need to set the permissions inside your Dockerfile:

$ cat df.vf-uid
FROM busybox
RUN mkdir -p /data && echo "hello world" > /data/hello && chown -R 1000 /data

$ docker build -t test-vf -f df.vf-uid .
Sending build context to Docker daemon 23.06 MB
Step 1 : FROM busybox
 ---> 2b8fd9751c4c
Step 2 : RUN mkdir -p /data && echo "hello world" > /data/hello && chown -R 1000 /data
 ---> Using cache
 ---> 41390b132940
Successfully built 41390b132940

$ docker run -v test-vol:/data --rm -it test-vf ls -alR /data
/data:
total 12
drwxr-xr-x    2 1000     root          4096 Sep 19 15:26 .
drwxr-xr-x   19 root     root          4096 Sep 19 15:26 ..
-rw-r--r--    1 1000     root            12 Aug 22 11:43 hello

Answer 2

If you use the new --mount syntax instead of the old -v/--volume syntax it is supposedly possible to assign a uid to the volume's contents via docker volume create somename --opt -o=uid=1000 or something similar.

See https://docs.docker.com/engine/reference/commandline/volume_create/#driver-specific-options

I haven't fully tested this to run as non-root or using the dockremap dynamic user with the userns-map option but hope to soon.