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Serial Device Not Detected on Linux (BRLTTY Conflict)

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Toby Chui edited this page Aug 3, 2026 · 1 revision

Troubleshooting: Serial Device Not Detected on Linux (BRLTTY Conflict)

On Linux systems with BRLTTY (Braille TTY / screen reader accessibility service) installed, the DezKVM-Go's USB-to-serial adapter may be claimed by BRLTTY before the OS can expose it as a standard serial device (e.g. /dev/ttyUSB0). As a result, the device does not appear in the "Connect Serial" device list in the DezKVM-Go control panel.

This is a known class of issue affecting CH340 / CH341 USB serial chips, which is used in the hardware of DezKVM-Go.

Affected Systems

BRLTTY is included by default in many Debian-based distributions, including:

  • Ubuntu
  • Linux Mint
  • Zorin OS
  • Other Debian derivatives

If your distribution ships BRLTTY as part of its default accessibility packages, you may be affected as well.

Environment Where Issue Was Confirmed

Component Detail
Device DezKVM-Go (Generation 3)
Host OS Zorin OS 18.1 (Ubuntu-based)
Browser Brave 1.92.144 (Chromium 150.0.7871.186), or any WebSerial-enabled browser
BRLTTY Version 6.6 (rev BRLTTY-6.6)

Symptom

When opening the DezKVM-Go control panel and selecting Connect Serial, no USB serial device (e.g. USB Serial (ttyUSB0)) appears in the device list.

Diagnosis

1. Confirm the device is detected by the system

lsusb | grep -i CH340

Expected output:

Bus 001 Device 024: ID 1a86:7523 QinHeng Electronics CH340 serial converter

2. Check for the serial device node

ls /dev/ttyUSB*

If affected, this returns:

ls: cannot access '/dev/ttyUSB*': No such file or directory

3. Check kernel/USB logs for a BRLTTY conflict

sudo dmesg -w

Look for a sequence similar to:

ch341 1-6.2.3:1.0: ch341-uart converter detected
usb 1-6.2.3: ch341-uart converter now attached to ttyUSB0
input: BRLTTY 6.6 Linux Screen Driver Keyboard as /devices/virtual/input/input25
usb 1-6.2.3: usbfs: interface 0 claimed by ch341 while 'brltty' sets config #1
ch341-uart ttyUSB0: ch341-uart converter now disconnected from ttyUSB0
ch341 1-6.2.3:1.0: device disconnected

This confirms BRLTTY is claiming the interface immediately after the kernel driver attaches it, which detaches the ttyUSB0 node.

Resolution

Update BRLTTY's udev rules so it ignores the CH340/CH341 device, allowing the standard kernel driver to keep control of it.

⚠️ Before proceeding, verify these assumptions on your own system:

  • Your device uses VID/PID 1a86:7523 (check with lsusb | grep -i CH340)
  • BRLTTY's udev rules file is at /usr/lib/udev/rules.d/85-brltty.rules (check with sudo find / -name "*brltty*.rules" 2>/dev/null)

Steps

  1. Copy the BRLTTY rules file to /etc/udev/rules.d/ so your change survives package updates:
   sudo cp /usr/lib/udev/rules.d/85-brltty.rules /etc/udev/rules.d/
  1. Comment out the line matching the CH340/CH341 device (VID/PID 1a86:7523):
   sudo sed -e '/^[^#]/ s/\(^.*1a86\/7523.*$\)/#\1/' -i /etc/udev/rules.d/85-brltty.rules
  1. Reload udev rules:
   sudo udevadm control --reload-rules

  1. Physically disconnect and reconnect the DezKVM-Go device.

  2. Reload the DezKVM-Go control panel page and try Connect Serial again.

Alternative

If you don't rely on BRLTTY / Braille display accessibility features, you can instead remove the BRLTTY package entirely.

References

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