Docker Guide

The Best Docker Setup

TL; DR: An eponymous user per daemon and a shared group with a umask of 002. Consistent path definitions between all containers that maintains the folder structure. Using one volume for Sonarr, Radarr and Lidarr so the download folder and library folder are on the same file system which makes hard links and instant moves possible. And most of all, ignore most of the Docker image’s path documentation!

Introduction

This article will not show you specifics about the best Docker setup, but it describes an overview that you can use to make your own setup the best that it can be. The idea is that you run each docker container as its own user, with a shared group and consistent volumes so every container sees the same path layout. This is easy to say, but difficult to understand and explain.

Multiple users and a shared group

Permissions

Ideally, each software runs as its own user user and they’re all part of a shared group with folder permissions set to 775 (drwxrwxr-x) and files set to 664 (-rw-rw-r--), which is a umask of 002. A sane alternative to this is a single shared user, which would use 755 and 644 which is a umask of 022. You can restrict permissions even more by denying read from “other”, which would be a umask of 007 for a user per daemon or 077 for a single shared user. For a deeper explanation, try the Arch Linux wiki articles about File permissions and attributes and Umask.

UMASK

Many docker images accept a -e UMASK=002 environment variable and some software inside can be configured with a user, group and umask (NZBGet) or folder/file permission (Sonarr/Radarr). This will ensure that files and folders created by one can be read and written by the others. If you’re using existing folders and files, you’ll need to fix their current ownership and permissions too, but going forward they’ll be correct because you set each software up right.

PUID and PGID

Many docker images also take a -e PUID=123 and -e PGID=321 that lets you change the UID/GID used inside to that of an account on the outside. If you ever peak in, you’ll find that username is something like abc, nobody or hotio, but because it uses the UID/GID you pass in, on the outside it looks like the expected user. If you’re using storage from another system via NFS or CIFS, it will make your life easier if that system also has matching users and group. Perhaps let one system pick the UID/GIDs, then re-use those on the other system, assuming they don’t conflict.

Example

You run Sonarr using hotio/sonarr, you’ve created a sonarr user with uid 123 and a shared group media with gid 321 which the sonarr user is a member of. You configure the Docker image to run with -e PUID=123 -e PGID=321 -e UMASK=002. Sonarr also lets you configured user, group as well as folder and file permissions. The previous settings should negate these, but you could configure them if you wanted. Folders would be 775, files 664 and the user/group are a little tricky because inside the container, they have a different name. Maybe abc or nobody. I’d leave all these blank unless you find you need them for some reason.

Single user and optional shared group

Another popular and arguably easier option is a single, shared user. Perhaps even your user. It isn’t as secure and doesn’t follow best practices, but in the end it is easier to understand and implement. The UMASK for this is 022 which results in 755 (drwxr-xr-x) for folders and 644 (-rw-r--r--) for files. The group no longer really matters, so you’ll probably just use the group named after the user. This does make it harder to share with other users, so you may still end up wanting a UMASK of 002 even w/ this setup.

Ownership and permissions of /config

Don’t forget that your /config volume will also need to have correct ownership and permissions, usually the daemon’s user and that user’s group like sonarr:sonarr and a umask of 022 or 077 so only that user has access. In a single user setup, this would of course be the one user you’ve chosen.

Consistent and well planned paths

The easiest and most important detail is to create unified path definitions across all the containers.

If you’re wondering why hard links aren’t working or why a simple move is taking far longer than it should, this section explains it. The paths you use on the inside matter. Because of how Docker’s volumes work, passing in two volumes such as the commonly suggested /tv and /downloads makes them look like two file systems, even if they aren’t. This means hard links won’t work and instead of an instant move, a slower and more io intensive copy + delete is used. If you have multiple download clients because you’re using torrents and usenet, having a single /downloads path means they’ll be mixed up. Because the Radarr in one container will ask the NZBGet in its own container where files are, using the same path in both means it will all just work. If you don’t, you’d need to fix it with a remote path map.

So pick one path layout and use it for all of them. I’m a fan of /data, but there are other great names like /shared, /media or /dvr. If this can be the same on the outside and inside, your setup will be simpler: one path to remember or if integrating docker and native software. But if not, that’s fine too. For example, Synology might use /Volume1/data and unRAID might use /mnt/user/data on the outside, but /data on the inside is fine.

It is also important to remember that you’ll need to setup or re-configure paths in the software running inside these Docker containers. If you change the paths for your download client, you’ll need to edit its settings to match. If you change your library path, you’ll need to change those settings in Sonarr, Radarr, Lidarr and/or Plex.

Examples

What matters here is the general structure, not the names. You are free to pick folder names that make sense to you. And there are other ways of arranging things too. For example, you’re not likely to download and run into conflicts of identical releases between usenet and torrents, so you could put both in /data/downloads/{movies|music|tv} folders. Downloads don’t even have to be sorted into sub-folders either, since movies, music and tv will rarely conflict.

This example data folder has sub-folders for torrents and usenet and each of these have sub-folders for tv, movie and music downloads to keep things neat. The media folder has nicely named TV, Movies and Music sub-folders, this is your library and what you’d pass to Plex or Emby.

data
├── torrents
│  ├── movies
│  ├── music
│  └── tv
├── usenet
│  ├── movies
│  ├── music
│  └── tv
└── media
    ├── Movies
    ├── Music
    └── TV

The path for each Docker container can be as specific as needed while still maintaining the correct structure:

Torrents

data
└── torrents
    ├── movies
    ├── music
    └── tv

Torrents only needs access to torrent files, so pass it -v /host/data/torrents:/data/torrents. In the torrent software settings, you’ll need to reconfigure paths and you can sort into sub-folders like/data/torrents/{tv|movies|music}.

Usenet

data
└── usenet
    ├── movies
    ├── music
    └── tv

Usenet only needs access to usenet files, so pass it -v /host/data/usenet:/data/usenet. In the usenet software settings, you’ll need to reconfigure paths and you can sort into sub-folders like/data/usenet/{tv|movies|music}.

Media Server

data
└── media
    ├── Movies
    ├── Music
    └── TV

Plex/Emby only needs access to your media library, so pass -v /host/data/media:/data/media, which can have any number of sub folders like Movies, Kids Movies, TV, Documentary TV and/or Music as sub folders.

Sonarr, Radarr and Lidarr

data
├── torrents
│  ├── movies
│  ├── music
│  └── tv
├── usenet
│  ├── movies
│  ├── music
│  └── tv
└── media
    ├── Movies
    ├── Music
    └── TV

Sonarr, Radarr and Lidarr get everything using -v /host/data:/data because the download folder(s) and media folder will look like and be one file system. Hard links will work and moves will be atomic, instead of copy + delete.

Issues

There are a couple minor issues w/ not following the Docker image’s suggested paths.

The biggest is that volumes defined in the Dockerfile will get created if they’re not specified, this means they’ll pile up as you delete and re-create the containers. If they end up w/ data in them, they can consume space unexpectedly and likely in an unsuitable place. You can find a cleanup command in the helpful commands section below. This could also be mitigated by passing in an empty folder for all the volumes you don’t want to use, like /data/empty:/movies and /data/empty:/downloads. Maybe even put a file named DO NOT USE THIS FOLDER inside, to remind yourself.

Another problem is that some images are pre-configured to use the documented volumes, so you’ll need to change settings in the software inside the Docker container. Thankfully, since configuration persists outside the container this is a one time issue. You might also pick a path like /data or /media which some images already define for a specific use. It shouldn’t be a problem, but will be a little more confusing when combined w/ the previous issues. In the end, it is worth it for working hard links and fast moves. The consistency and simplicity are welcome side effects as well.

If you use the latest version of the abandoned RadarrSync to synchronize two Radarr instances, it depends on mapping the same path inside to a different path on the outside, for example /movies for one instance would point at /data/media/Movies and the other at /data/media/Movies 4k. This breaks everything you’ve read above. There is no good solution, you either use the old version which isn’t as good, do your mapping in a way that is ugly and breaks hard links or just don’t use it at all.

Running containers using

Docker-compose

This is the best option for most users, it lets you control and configure many containers and their interdependence in one file. A good starting place is docker’s own Get started with Docker Compose. You can use composerize or red5d/docker-autocomposeto convert docker run commands into a single docker-compose.yml file.

The below is not a complete working example! The containers only have PID, UID, UMASK and example paths defined to keep it simple.

# sonarr
Sonarr:
    image: "hotio/sonarr"
    volumes:
        - /path/to/config/sonarr:/config
        - /host/data:/data
    environment:
        - PUID=111
        - PGID=321
        - UMASK=002

# deluge
Deluge:
    image: binhex/arch-delugevpn
    volumes:
        - /path/to/config/deluge:/config
        - /host/data/torrents:/data/torrents
    environment:
        - PUID=222
        - PGID=321
        - UMASK=002

# sabnzbd
SABnzbd:
    image: binhex/arch-sabnzbd
    volumes:
        - /path/to/config/sabnzbd:/config
        - /host/data/usenet:/data/usenet
    environment:
        - PUID=333
        - PGID=321
        - UMASK=002

# plex
Plex:
    image: binhex/arch-plex
    volumes:
        - /path/to/config/plex:/config
        - /host/data/media:/data/media

    environment:
        - PUID=444
        - PGID=321
        - UMASK=002

Update all images and containers

docker-compose pull
docker-compose up -d

Update individual image and container

docker-compose pull NAME
docker-compose up -d NAME

Docker Run

Like the Docker Compose example above, the following docker run commands are stripped down to only the PUID, PGID, UMASK and volumes in order to act as an obvious example.

# sonarr
docker run -v /path/to/config/sonarr:/config \
           -v /host/data:/data \
           -e PUID=111 -e PGID=321 -e UMASK=002 \
           hotio/sonarr

# deluge
docker run -v /path/to/config/deluge:/config \
           -v /host/data/torrents:/data/torrents \
           -e PUID=222 -e PGID=321 -e UMASK=002 \
           binhex/arch-delugevpn

# sabnzbd
docker run -v /path/to/config/sabnzbd:/config \
           -v /host/data/usenet:/data/usenet \
           -e PUID=333 -e PGID=321 -e UMASK=002 \
           binhex/arch-sabnzbd

# plex
docker run -v /path/to/config/plex:/config \
           -v /host/data/media:/data/media \
           -e PUID=444 -e PGID=321 -e UMASK=002 \
           binhex/arch-plex

Systemd

I don’t run a full Docker setup, so I manage my few Docker containers with individual systemd service files. It standardizes control and makes dependencies simpler for both native and docker services. The generic example below can be adapted to any container by adjusting or adding the various values and options.

# /etc/systemd/system/thing.service
[Unit]
Description=Thing
Requires=docker.service
After=network.target docker.service

[Service]
ExecStart=/usr/bin/docker run --rm \
                          --name=thing \
                          -v /path/to/config/thing:/config \
                          -v /host/data:/data
                          -e PUID=111 -e PGID=321 -e UMASK=002 \
                          nobody/thing

ExecStop=/usr/bin/docker stop -t 30 thing

[Install]
WantedBy=default.target

Helpful commands

List running containers

docker ps

Shell inside a container

docker exec -it CONTAINER_NAME /bin/bash

For more information, see the docker exec documentation.

Prune docker

docker system prune --all --volumes

Remove unused containers, networks, volumes, images and build cache. As the WARNING this command gives says, this will remove all of the previously mentioned items for anything not in use by a running container. In a correctly configured environment, this is fine. But be aware and proceed cautiously the first time. See the docker system prune documentation for more details.

Get docker run command

Getting the docker run command from GUI managers can be hard, this docker image makes it easy for a running container (source).

docker run --rm -v /var/run/docker.sock:/var/run/docker.sock assaflavie/runlike CONTAINER_NAME

Get docker-compose

Getting a docker-compose.yml from running instances is possible w/ red5d/docker-autocompose, in case you’ve already started your containers w/ docker run or docker create and want to change to docker-compose style. It is also great for sharing your settings with others, since it doesn’t matter what management software you’re using.

docker run --rm -v /var/run/docker.sock:/var/run/docker.sock red5d/docker-autocompose CONTAINER_NAME [CONTAINER_NAME] ... [CONTAINER_NAME]

Troubleshoot networking

Most Docker images don’t have many useful tools in them for troubleshooting, but you can attach a network troubleshooting type image to an existing container to help with that.

docker run -it --rm --network container:CONTAINER_NAME nicolaka/netshoot

Recursively chown user and group

chown -R user:group /some/path/here

Recursively chmod to 775/664

chmod -R a=,a+rX,u+w,g+w /some/path/here
          ^  ^    ^   ^ adds write to group
          |  |    | adds write to user
          |  | adds read to all and execute to all folders (which controls access)
          | sets all to `000`

Find UID/GID for user

id <username>

Examine files for hard links

ls -alhi
42207934 -rw-r--r--  2 user group    0 Sep 11 11:55 hardlink
42207936 -rw-r--r--  1 user group    0 Sep 11 11:55 nohardlinks
42207934 -rw-r--r--  2 user group    0 Sep 11 11:55 original

stat original
  File: original
  Size: 0               Blocks: 0          IO Block: 4096   regular empty file
Device: 803h/2051d      Inode: 42207934    Links: 2
Access: (0644/-rw-r--r--)  Uid: ( 1000/ user)   Gid: ( 1001/ group)
Access: 2020-09-11 11:55:43.803327144 -0500
Modify: 2020-09-11 11:55:43.803327144 -0500
Change: 2020-09-11 11:55:49.706660476 -0500
 Birth: 2020-09-11 11:55:43.803327144 -0500

Interesting docker images

• rasmunk/sshfs let you create an sshfs volume, perfect for a seedbox setup using a remote mount instead of sync. Better documentation, including examples can be found at the github rasmunk/docker-volume-sshfs repository. This is a more recently maintained fork of vieux/sshfs.
• hotio’s sonarr, radarr and lidarr images let you run the built in version or specify an alternative via environment variable. The documentation and Dockerfile also don’t make any poor path suggestions.
• hotio’s ombi, jackett, nzbhydra2 and bazarr are useful too, but don’t really require any special permissions or paths.
• hotio’s unpackerr is useful for packed torrent extraction across a variety of torrent clients where unpacking is lacking or missing entirely.
• binhex’s qbittorrent, deluge and rtorrent are popular torrent clients with built in VPN support. For usenet, there is sabnzbd and nzbget.
• binhex’s sonarr, radarr and lidarr images suggest default paths that don’t allow for hard linking, instead follow the process described above and pass in a single volume.
• linuxserver.io’s images also suggest default paths that don’t allow for hard linking, instead follow the process described above and pass in a single volume. But they do have images for a lot of software and they’re well maintained.
• pyouroboros/ouroboros or containrrr/watchtower automatically update your running Docker containers to the latest available image. These are not recommended if you use Docker Compose.

Custom Docker Network and DNS

One interesting feature of a custom Docker network is that it gets its own DNS server. If you create a bridge network for your containers, you can use their hostnames in your configuration. For example, if you docker run --network=isolated --hostname=deluge binhex/arch-deluge and docker run --network=isolated --hostname=radarr binhex/arch-radarr, you can then configure the Download Client in Radarr to point at just deluge and it’ll work and communicate on its own private network. Which means if you wanted to be even more secure, you could stop forwarding that port too. If you put your reverse proxy container on the same network, you can even stop forwarding the web interface ports and make them even more secure.

Common Problems

Correct outside paths, incorrect inside paths

Many people read this and think they understand, but they end up seeing the outside path correctly to something like /data/usenet, but then they miss the point and set the inside path to /downloads still.

Running Docker containers as root or changing users around

If you find yourself running your containers as root:root, you’re doing something wrong. If you’re not passing in a UID and GID, you’ll be using what ever the default is for the image and that will be unlikely to line up w/ a reasonable user on your system. And if you’re changing the user and group your Docker containers are running as, you’ll probably end up w/ permissions issues on folders like the /config folder which will likely have files and folders in them that got created the first time w/ the UID/GID you used the first time.

Running Docker containers w/ umask 000

If you find yourself setting a UMASK of 000 (which is 777 for folders and 666 for files), you’re also doing something wrong. It leaves your files and folders read/write to everyone, which is poor Linux hygiene.

LinuxServer.io

The entire reason this article even exists is linuxserver.io’s documentation and default path suggestions. They’re singlehandedly responsible for the /tv, /movies and /downloads paths which break hard links and atomic moves. It is for this reason that none of them are specifically recommended by this article. That said, once you understand the problem with those paths and that you don’t have to use them, their images are fine. So feel free to use them and most of their documentation. Just ignore their path suggestions.

Getting Help

Need some help? For real time, chat style support try the Sonarr or Radarr Discord servers. If you prefer forum style support, make a post in /r/sonarr or /r/radarr.