Hardware transcoding not working due to incorrect permissions

[Lester Sanchez]

Expected Behavior

On a device with Intel QuickSync, when /dev/dri is correctly mapped, Plex should use /dev/dri/renderD128 for hardware transcoding.

Current Behavior

Hardware transcoding not working due to permissions issue.

docker-compose.yml

version: "2.1"
services:
  plex:
    container_name: plex
    image: cr.hotio.dev/hotio/plex
    devices:
      - /dev/dri:/dev/dri
    environment:
      - PUID=1000
      - PGID=1000
      - UMASK=002
      - TZ=Europe/London
      - PLEX_CLAIM=claim-REDACTED
      - PLEX_PASS=yes
    volumes:
      - /appdata/plex/config:/config
      - /appdata/plex/transcode:/transcode
      - /data/media:/media
    ports:
      - 32400:32400
    restart: unless-stopped

$ docker exec -it plex bash
$ ls -la /dev/dri
total 0
drwxr-xr-x 2 root   root        80 Nov  5 19:26 .
drwxr-xr-x 6 root   root       360 Nov  5 19:26 ..
crw-rw---- 1 nobody video 226,   0 Nov  5 19:24 card0
crw-rw---- 1 nobody   108 226, 128 Oct 31 16:13 renderD128

$ id hotio
uid=1000(hotio) gid=1000(hotio) groups=1000(hotio),100(users)

• Device /dev/dri/renderD128 should be owned by group render that doesn't exist.
• User hotio should be member of render group.

As a result, Plex fails to use /dev/dri/renderD128 to do hardware trancoding, with following message in the logs

DEBUG - [Req#14f/Transcode] Codecs: hardware transcoding: opening hw device failed - probably not supported by this system, error: Generic error in an external library
DEBUG - [Req#14f/Transcode] Could not create hardware context for hevc

Steps to Reproduce

See above

Workaround

$ docker exec -it plex bash
$ groupadd -g 108 render
$ usermod -aG render hotio
$ exit
$ docker restart plex

These changes don't survive a system restart. When container is destroyed, these changes are lost.

Environment

Ubuntu 22.04.1 LTS (GNU/Linux 5.15.64-1-pve x86_64)

[Lester Sanchez]

After further investigation, I found the command

find /dev/dri /dev/dvb -type c -print 2>/dev/null

returns nothing when run within the container. Because of that, the script https://github.com/hotio/plex/blob/release/root/etc/cont-init.d/04-hw-support fails to create the missing group for the relevant devices.

When removing -type c from the command above, it returns the relevant devices + parent directory

$ find /dev/dri /dev/dvb -type c -print 2>/dev/null
<nothing printed>

$ find /dev/dri /dev/dvb -print 2>/dev/null
/dev/dri
/dev/dri/renderD128
/dev/dri/card0

but when called with -type f, it displays the expected output

$ find /dev/dri /dev/dvb -type f -print 2>/dev/null
/dev/dri/renderD128
/dev/dri/card0

[mrhotio]

Can't reproduce on my system

[Lester Sanchez]

Very strange. I just created a fresh new host (LXC) with Ubuntu 18.04 (in case it was an issue with recent Ubuntu version) and could reproduce, using the same docker-compose.yml I posted before.

root@hotioplex:/docker# docker exec -it plex bash
root@6adb555c49dc:/# ls -la /dev/dri
total 0
drwxr-xr-x 2 root   root        80 Nov  6 19:53 .
drwxr-xr-x 6 root   root       360 Nov  6 19:53 ..
crw-rw---- 1 nobody video 226,   0 Nov  6 09:48 card0
crw-rw---- 1 nobody   108 226, 128 Oct 31 16:13 renderD128
root@6adb555c49dc:/# find /dev/dri /dev/dvb -type c -print 2>/dev/null
root@6adb555c49dc:/# find /dev/dri /dev/dvb -type f -print 2>/dev/null
/dev/dri/renderD128
/dev/dri/card0