Document using cgroup rules to start container without USB

[LongLiveCHIEF]

from https://discordapp.com/channels/704958479194128507/753995646218010674/792045233600856066

I have this problem where I can't restart the octoprint docker if my printer is not on. Anyone else struggled with this?
In a nutshell: If my printer is OFF, the /dev/ttyACM0 is not available > octoprint container fails to mount it during startup > octoprint container fails to start.
I currently have to turn the printer ON via smart socket and only then start/restart the octoprint container.
It's fairly small annoyance, but I'd prefer octoprint to always be on and printer itself to be controlled via smart socket. Is this possible?

Powering off the printer octoprint controls during idle time is a common requirement of OctoPrint users. Docker will fail to start if you try to pass it a usb serial device if that device does not yet exist, and in addition, the device could be assigned a different binding depending on what usb port its plugged into or what order that usb device is booted.

The solution here will be to create a custom cgroup-rule, mount that, and create a udev rule which adds the device to the container when it is added. see: Dealing with dynamically created devices (--device-cgroup-rule)

The issue here of course is that the user may not be using a static name for the octoprint container, so this may only work in circumstances where you're using docker run or docker-compose with an container_name

[LongLiveCHIEF]

The real challenge here is not adding the cgroup rule, but the fact that you have to know the state of the desired device when the container starts. If it is connected, you need to include the device in the container startup. If it isn't, then having added the udev rule will cause the device to be added when it is detected.

This is just as bad as trying to start a container without the device, because it means you have to know the state of the printer prior to container startup regardless of if you have these device rules in place.

You could easily create a systemd unit file that uses a script to start the octoprint container, and that script checks for a device and includes it in container startup if it exists, but you've now once again tied the system to the container.

[LongLiveCHIEF]

Basically, we could support systemd type systems, and provide that script, and then tell anyone using portainer or any other tool that manages containers that they would be on their own to figure out how to do a dynamic container start?

[reverendj1]

I came across this Reddit post, https://www.reddit.com/r/octoprint/comments/klxzpr/docker_mapping_printer_to_usb_port/ and with your and wingjames' help was able to successfully set it up so that I can start Octoprint with the printer turned off. I was trying to think of a more elegant solution like you want and came across this, https://github.com/marthoc/docker-deconz/issues/298, where it seems that someone else is doing what you want. I couldn't quite figure out all the pieces to put it together or find in the code where they were setting up the devices or anything. Maybe it will point you in the right direction.

[Paraphraser]

@reverendj1 perhaps see this gist. It’s a brute force solution but it does actually work. I’m running OctoPrint in a Docker container on a Pi 3B+. I’ve also tested the approach on a Pi 4 with other detachable devices like a Zigbee adapter.

[LongLiveCHIEF]

I've already got the work for all this done, (it's a really simple single-line script for udev rules), just haven't had time to finish the PR to share docs.

[palsch]

Hello all, I had the same issue with my printer. Usually it is powered off. If I tried to restart my raspi or the octoprint container, it failed because of the missing usb device. So my current solution is also to use cgroup and mknod. I modified the Dockerfile and the docker-compose file with the following lines (my printer gets always ttyUSB0):

Dockerfile (take original Dockerfile and add following line before the ENTRYPOINT):

This command create a new script in the /etc/cont-init.d folder, that is executed automatically on container start (see also s6 overlay). The command mknod /dev/ttyUSB0 c 188 0 creates a new device file that can be used by octoprint to connect to the printer as soon as the printer is available. That means, the device file can be created while the printer is off.

....
RUN echo "#!/usr/bin/execlineb -P\nmknod /dev/ttyUSB0 c 188 0" >> /etc/cont-init.d/init-usb-device
ENTRYPOINT ["/init"]

Build the new docker image: docker build . -t octoprint-custom

docker-compose.yml (add following configuration changes to your existing file):

services:
  octoprint:
    image: octoprint-custom
    devices:
      - /dev/bus/usb # map the complete usb device bus
    volumes:
      - /run/udev:/run/udev:ro  # so that serial number vendor/product ids are known
    device_cgroup_rules:
      - 'c 188:* rmw' # allow creation of /dev/ttyUSBx nodes via mknod

[squirrel289]

I've already got the work for all this done, (it's a really simple single-line script for udev rules), just haven't had time to finish the PR to share docs.

Any chance you could share this one liner here so other less adept folks (like me) can use while you’re assembling the PR?

[LongLiveCHIEF]

https://github.com/OctoPrint/octoprint-docker/blob/udev-rules-for-dynamic-usb-serial-support/71-octoprint.docker.rules

[glennpierce]

https://github.com/OctoPrint/octoprint-docker/blob/udev-rules-for-dynamic-usb-serial-support/71-octoprint.docker.rules

Anything else needed other that adding this file to say /usr/lib/udev/rules.d and rebooting.
When starting the container I get the same error about missing ttyACM0

[jjaeggli]

An alternative solution I'm using to this script above is to create a wrapper init script in conjunction to the cgroup rules. There's nothing which says the character devices need to be added to the filesystem dynamically, given that the printer is the only serial device connected to this system. I've placed the script in the octoprint volume and it looks something like this:

#!/bin/sh

mknod c 166 0 /dev/ttyACM0
mknod c 166 1 /dev/ttyACM1

/init $@

On my system the Rambo board uses device major 166. I then execute the script using docker flag --entrypoint=/octoprint/init_usb.sh. This means that no changes are required to the existing image, and I can upgrade without any further time commitment.

[bambuleee]

https://github.com/OctoPrint/octoprint-docker/blob/udev-rules-for-dynamic-usb-serial-support/71-octoprint.docker.rules

Anything else needed other that adding this file to say /usr/lib/udev/rules.d and rebooting. When starting the container I get the same error about missing ttyACM0

Hi,
I tried a lot and finally got it working. You have to change the name of the dockercontainer (here octoprint-container) and the major and minor parameter (here 188 and 0-> ls /dev/ttyUSBDEVICE -l)

/etc/udev/rules.d/90-octoprint.rules

SUBSYSTEM!="tty", GOTO="end_octoprint_printers"
ACTION=="add|change", SUBSYSTEM=="tty", KERNEL=="ttyUSB[0-9]|ttyACM[0-9]", RUN+="/bin/bash /home/pi/drucker.sh"
ACTION=="remove", SUBSYSTEM=="tty", KERNEL=="ttyUSB[0-9]|ttyACM[0-9]", RUN+="/usr/bin/docker exec octoprint-container rm -rf /dev/ttyUSB0"
LABEL="end_octoprint_printers"

Script drucker.sh (chmod +x):

#!/bin/bash
minor=0
/usr/bin/docker exec octoprint-container rm -rf /dev/ttyUSB0
/usr/bin/docker exec octoprint-container mknod /dev/ttyUSB0 c 188 $minor

compose-file for octoprint

device_cgroup_rules:
  - 'c 188:* rmw'

[matt-laird]

I experienced some real pain and suffering trying to get this to work, but got there in the end.

• As @bambuleee mentioned in their post, the 71-octoprint.docker.rules should rather make a call to a script which executes the commands in the container, on an add|change event because I experienced problems with the RUN command that included both the removal and (&&) creation of the device in the container.

Notes for newbies:

Just a note for anyone finding this thread, here are a few unspoken things that are important, taking into account you have read the whole issue thread and are now here:

• The udev rules file needs to be saved on the host of your octoprint container.
• The number in the name of the udev rule does matter, just leave it as 71 you should be fine.
• Once the rules file is in place, reboot your OS for these to rules to take effect.
• Use the device_cgroup_rules directive in your compose to make sure the container can handle no solid references devices e.g. /dev/ttyACM0:/dev/ttyACM0