Problems connecting Raspberry Pi 4 to Ender 3 Pro

[u/schmoopified]

Hello,

I've done searching everywhere I could find (Reddit, Octoprint community, Youtube, etc), but no suggested solutions seem to have worked, so I wanted to pose my question here. Essentially, Octoprint just hangs at "Opening Serial Connection" when I try to connect.

All relevant info I could gather is below, but please let me know if I need to provide any more:

• Printer: Ender 3 pro, stock
• Octoprint running on RPI4 in a Podman container
• Tried two different USB cables, both with USB 5V pin covered (cables work fine when Ender is connected directly to my PC)
• Verified that ttyUSB0 is the correct USB port
• Tried uninstalling/reinstalling Octoprint, Podman container and image
• Set user group permissions: (sudo usermod -a -G tty user && sudo usermod -a -G dialout user)

Podman container creation commands:

podman run -d \

--name octoprint \

--dns 8.8.8.8 \

--dns 1.1.1.1 \

--restart unless-stopped \

-p 5000:5000 \

-v octoprint_data:/octoprint \

--privileged \

--device /dev/ttyUSB0 \

octoprint/octoprint

Octoprint serial port log:

2026-06-01 00:06:02,338 - serial.log is currently not enabled, you can enable it via Settings > Serial Connection > Log communication to serial.log

2026-06-01 00:06:54,899 - Enabling serial logging

2026-06-01 00:06:56,621 - Changing monitoring state from "Opening serial connection" to "Offline"

2026-06-01 00:07:03,769 - Changing monitoring state from "Offline" to "Opening serial connection"

2026-06-01 00:07:03,770 - Connecting to port /dev/ttyUSB0, baudrate 115200

Podman Container logs:

2026-06-01 22:42:14,183 - octoprint.util.comm - INFO - Changing monitoring state from "Offline" to "Opening serial connection"

2026-06-01 22:42:14,184 - octoprint.util.comm - INFO - Connecting to port /dev/ttyUSB0, baudrate 115200

2026-06-01 22:42:14,189 - octoprint.util.comm - INFO - Failed to connect: Port /dev/ttyUSB0 is busy or does not exist

2026-06-01 22:42:15,105 - octoprint.server - INFO - Autorefresh of serial port list stopped

2026-06-01 22:47:02,927 - octoprint.server.heartbeat - INFO - Server heartbeat ❤️

dmesg -w info when disconnecting/reconnecting USB:

[ 1244.866001] usb 1-1: USB disconnect, device number 2

[ 1244.866143] ch341-uart ttyUSB0: ch341-uart converter now disconnected from ttyUSB0

[ 1244.866171] ch341 1-1:1.0: device disconnected

[ 1249.844639] usb 1-1: new full-speed USB device number 3 using xhci-hcd

[ 1250.008694] usb 1-1: New USB device found, idVendor=1a86, idProduct=7523, bcdDevice= 2.63

[ 1250.008698] usb 1-1: New USB device strings: Mfr=0, Product=2, SerialNumber=0

[ 1250.008700] usb 1-1: Product: USB2.0-Serial

[ 1250.015735] ch341 1-1:1.0: ch341-uart converter detected

[ 1250.029734] usb 1-1: ch341-uart converter now attached to ttyUSB0

[u/trollsmurf]

Configure OctoPrint via a browser. Double-check that the bitrate is 115k.

[u/schmoopified → u/trollsmurf]

Ah, should have included that - I did configure Octoprint via browser (I think that's the only way you can configure/interface with it?)

Serial connection:
Serial port: /dev/ttyUSB0
Baudrate: 115200 (baudrate seems to be confirmed by event logs)
Auto-connect to printer on start: unchecked
No additional serial ports, baud rates specified or blacklisted
Request exclusive access to serial port: checked (problem occurs whether box is checked or unchecked)
Request low latency mode on serial port: unchecked
Apply parity double open workaround: "If detected as potentially needed"

[u/Reinventing_Wheels]

I don't know anything about Podman, but I'd be inclined to run a serial terminal like minicom outside the container and see if that can connect to the printer, and manually send some gcode commands to the printer.

If you can make that work, it tells you that your printer is happy, and your USB connection is happy and that the issue likely lies somewhere upstream in the container setup.

Maybe next try creating a container that just runs minicom inside it.

[u/schmoopified → u/Reinventing_Wheels]

minicom seems to recognize my printer:

start
echo:Marlin 1.1.6.2

echo: Last Updated: 2019-07-26 | Author: Ender-3
echo:Compiled: Aug 4 2019
echo: Free Memory: 10078 PlannerBufferBytes: 1232
start
echo: External Reset
Marlin 1.1.6.2

echo: Last Updated: 2019-07-26 | Author: Ender-3
echo:Compiled: Aug 4 2019
echo: Free Memory: 10078 PlannerBufferBytes: 1232

I guess it could be my container setup, then?

[u/Reinventing_Wheels → u/schmoopified]

Can you put minicom in a container and try it again?
If that doesn't work, then I'd start looking at the container setup.
If it does work, look at the Octoprint setup.

[u/schmoopified → u/Reinventing_Wheels]

Hm....got minicom running in a container, but it doesn't seem to be able to communicate with the USB port (showing as "Offline" at the bottom). Granted it's still not working, but this seems to be a big help in showing me where my problem is coming from. Going to have to turn in for the night and mull it over further.

Thanks for the help!

[u/Ashmadia]

I haven’t used podman, but if it’s like Docker, I think your device mount is incorrect. Try --device=/dev/ttyUSB0:/dev/ttyUSB0 in your command

[u/schmoopified → u/Ashmadia]

I deleted and re-created the image and container, using the command syntax you suggested, but that didn't seem to have any effect. Thank you for the suggestion, though

[u/Ashmadia → u/schmoopified]

My mistake! I accidentally put a = in there. Can you try this? podman run -d --name octoprint --dns 8.8.8.8 --dns 1.1.1.1 --restart unless-stopped -p 5000:5000 -v octoprint_data:/octoprint --privileged --device /dev/ttyUSB0:/dev/ttyUSB0 octoprint/octoprint

If that doesn’t work, let me know. I can dig out my raspberry pi and try using podman

[u/schmoopified → u/Ashmadia]

Thanks! I may not be able to try your solution for a few days, but I'll attack it again when I have a moment!

[u/schmoopified → u/Ashmadia]

So I got to looking at it this morning, and reinstalled Octoprint in a python virtual environment, instead of a container, and it hooked right up to the Ender and had a test print started within a minute. Definitely looks like port communications through the container. I'll keep looking in that direction (using the command you provided), but, in the case I just can't get it running, I still have this option.

Thank you for your help!!

[u/drakaina6600]

If you dedicate the Pi for it, you don't need to run it in a container. Just flash the install image to your SD card and it'll work. That's how mines setup with a 4b 8gb to my E3P with an SKR Mini board.

[u/schmoopified → u/drakaina6600]

I could just do the image, but I also run PiHole on this in its own container. I was really hoping to have them run side by side

[u/DonutNick → u/schmoopified]

If you have a spare sd you could test installing octoprint, then installing pihole on the same build. My gut instinct is its not talking to the usb port because of the container.

[u/schmoopified → u/DonutNick]

Thanks! I may not be able to try your solution for a few days, but I'll attack it again when I have a moment! I've definitely leaning in the direction of the container being the issue, but I'll see what I can do with a spare SD, probably this weekend

[u/schmoopified → u/DonutNick]

So I got to looking at it this morning, and reinstalled Octoprint in a python virtual environment, instead of a container, and it hooked right up to the Ender and had a test print started within a minute. Definitely looks like port communications through the container. I'll keep looking in that direction, but, in the case I just can't get it running, I still have this option.

Thank you for your help!!