Unable to mount files in Docker

Question

Error description

I'm unable to mount files in Vagrant or Docker, so it seems like it's an issue caused by some kind of a permission error.
My OS is Ubuntu 18.04 LTS (Bionic Beaver), I'm not running any access control modules like SELinux as far as I'm aware.

The Vagrant-related discussion of the error is found in another question: Unable to mount files in Vagrant

Troubleshooting Docker

I'm unable to mount files into a Docker container with docker-compose, I'm trying to build: https://github.com/fredrikaverpil/saltstack-docker

I set my volumes in the docker-compose file to:

volumes:
  - ${PWD}/assets/master/etc/supervisor:/etc/supervisor
  - ${PWD}/assets/master/etc/salt:/etc/salt
  - ${PWD}/assets/master/var/cache/salt:/var/cache/salt
  - ${PWD}/assets/master/var/log/salt:/var/log/salt
  - ${PWD}/assets/master/srv:/srv

Yet I'm getting this output when running docker-compose up:

Creating network "saltstack_default" with the default driver
Creating salt_image
Creating salt
Creating minion
Attaching to salt, minion, salt_image
salt      | Error: could not find config file /etc/supervisor/supervisord.conf
salt      | For help, use /usr/bin/supervisord -h
salt exited with code 2
salt_image exited with code 0
minion    | [ERROR   ] DNS lookup of 'salt' failed.
minion    | [ERROR   ] Master hostname: 'salt' not found. Retrying in 30 seconds

docker inspecting the container shows correct configuration:

   "Mounts": [
        {
            "Type": "bind",
            "Source": "/somedir/saltstack/assets/master/etc/salt",
            "Destination": "/etc/salt",
            "Mode": "rw",
            "RW": true,
            "Propagation": "rprivate"
        },
        {
            "Type": "bind",
            "Source": "/somedir/saltstack/assets/master/var/cache/salt",
            "Destination": "/var/cache/salt",
            "Mode": "rw",
            "RW": true,
            "Propagation": "rprivate"
        },
        {
            "Type": "bind",
            "Source": "/somedir/saltstack/assets/master/etc/supervisor",
            "Destination": "/etc/supervisor",
            "Mode": "rw",
            "RW": true,
            "Propagation": "rprivate"
        },
        {
            "Type": "bind",
            "Source": "/somedir/saltstack/assets/master/var/log/salt",
            "Destination": "/var/log/salt",
            "Mode": "rw",
            "RW": true,
            "Propagation": "rprivate"
        },
        {
            "Type": "bind",
            "Source": "/somedir/saltstack/assets/master/srv",
            "Destination": "/srv",
            "Mode": "rw",
            "RW": true,
            "Propagation": "rprivate"
        }

But entering the container (with another entrypoint command), shows that the files that are supposed to be mounted are missing:

[root@salt /]# ll /etc/supervisor
total 0
[root@salt /]# ll /etc/salt
total 0
[root@salt /]# ll /var/cache/salt
total 0
[root@salt /]# ll /var/log/salt
total 0
[root@salt /]# ll /srv
total 0

Conclusion

It seems something is very messed up on my local machine when it comes to copying over files, possibly has to do with how my user is configured and what access it has to mounting files into VMs and containers.
If anyone can shed some light on this I'd appreciate it.

Updates

Update 1

I'm suspecting this is an issue with old stuff in /var/lib/docker which I'm about to remove, but before that here's another error I'm getting, maybe some kind of permission error:

> cat docker-compose.yml 
# based on https://docs.docker.com/samples/library/nginx/#using-environment-variables-in-nginx-configuration
version: '2'

services:
  web:
    image: nginx
    volumes:
     - ./testfile.txt:/etc/nginx/
    ports:
     - "8080:80"
    environment:
     - NGINX_HOST=foobar.com
     - NGINX_PORT=80
    command: /bin/bash -c "nginx -g 'daemon off;'"

> docker-compose up
Creating network "docker_compose-mounting_issue_default" with the default driver
Creating docker_compose-mounting_issue_web_1 ... error

ERROR: for docker_compose-mounting_issue_web_1  Cannot start service web: b'OCI runtime create failed: container_linux.go:348: starting container process caused "process_linux.go:402: container init caused \\"rootfs_linux.go:58: mounting \\\\\\"/home/.../troubleshoot/docker_compose-mounting_issue/testfile.txt\\\\\\" to rootfs \\\\\\"/var/lib/docker/aufs/mnt/580b79241399e838c67b74021ecf2597aade5f1711811f4ab5c9c7bbcd188449\\\\\\" at \\\\\\"/var/lib/docker/aufs/mnt/580b79241399e838c67b74021ecf2597aade5f1711811f4ab5c9c7bbcd188449/etc/nginx\\\\\\" caused \\\\\\"not a directory\\\\\\"\\"": unknown: Are you trying to mount a directory onto a file (or vice-versa)? Check if the specified host path exists and is the expected type'

ERROR: for web  Cannot start service web: b'OCI runtime create failed: container_linux.go:348: starting container process caused "process_linux.go:402: container init caused \\"rootfs_linux.go:58: mounting \\\\\\"/home/.../troubleshoot/docker_compose-mounting_issue/testfile.txt\\\\\\" to rootfs \\\\\\"/var/lib/docker/aufs/mnt/580b79241399e838c67b74021ecf2597aade5f1711811f4ab5c9c7bbcd188449\\\\\\" at \\\\\\"/var/lib/docker/aufs/mnt/580b79241399e838c67b74021ecf2597aade5f1711811f4ab5c9c7bbcd188449/etc/nginx\\\\\\" caused \\\\\\"not a directory\\\\\\"\\"": unknown: Are you trying to mount a directory onto a file (or vice-versa)? Check if the specified host path exists and is the expected type'
ERROR: Encountered errors while bringing up the project.

Update 2

So I removed everything in /var/lib/docker/ and it now works as it should, mounting my files. It was probably broken somewhere. Another suggestion I came across was giving permissions to the directory, chmod 777 seemed to help some users but I don't think this is that safe..

Answer 1

what folder permission that the user has(the one you are logged into run the docker-compose command), if that is is root user or the user has access to the folders and please change the ${PWD} to the relative/absolute path of the folder(one which you want to mount to container). docker-compose cant understand the ${PWD} env variable.

Ex: if you want to mount

${PWD}/assets/master/etc/supervisor:/etc/supervisor

it should be

./assets/master/etc/supervisor:/etc/supervisor