Docker from snap on Ubuntu can't create a shared bind mount

General
1

I am trying to mount a FUSE virtual filesystem from inside a Docker container and expose the mount point to the host.

Docker is installed via snap on Ubuntu 20.04

The software is a fresh install of [Seafile][1] (a Dropbox alternative), but this problem I believe is more related to Docker, snap, and mounting file systems on Ubuntu. For what it’s worth, I was following the official instructions [here][2].

Inside the container (when it runs successfully), a script mounts a FUSE virtual filesystem to /seafile-fuse that makes the all files stored within Seafile visible.

docker-compose.yml exerpt:

version: '3.3'
services: 
  seafile:
    image: seafileltd/seafile-mc:latest
    container_name: seafile
    volumes:
      - /home/jonathan/seafile/seafile-data:/shared
      - type: bind
        source: /home/jonathan/seafile/seafile-fuse
        target: /seafile-fuse
        bind:
          propagation: rshared
    privileged: true
    cap_add:
      - SYS_ADMIN

This leads to:

ERROR: for seafile  Cannot start service seafile: path /home/jonathan/seafile/seafile-fuse is mounted on /home but it is not a shared mount

I found this question on StackOverflow which hints that the issue may to do with the docker daemon running in a different namespace.

What do I need to do to connect the host directory /home/jonathan/seafile/seafile-fuse so that it sees the container directory /seafile-fuse?

Bonus question…

Given that this is to be an internet facing home-server, is it necessary this this becomes a privileged container? Are there better options?

Thanks!!

I have described the situation on the Seafile forums Official Instructions for FUSE Extension in Docker leads to errors - Seafile Server - Seafile Community Forum

2

The Snap Docker package is a “different thing”. It may be named Docker and have shared the same code base at one point like vanila Docker does, but is bend like hell to align with Snaps philosophy. I personaly consider the Snap version broken…

You might want to raise this issue either in an Ubuntu or Snap forum, or consider to replace the Snap package with vanilla Docker from Docker’s apt repositores.