# Ender 3: Lost communication with MCU 'mcu' **URL:** \ **Category:** General Discussion\ **Created:** [December 1, 2023, 4:51am UTC](https://klipper.discourse.group/t/ender-3-lost-communication-with-mcu-mcu/11981 "2023-12-01T04:51:47Z")\ **Posts on this page:** 1\ **Showing post:** 4
**Author:** ![JassMan23](https://yyz2.discourse-cdn.com/free1/user_avatar/klipper.discourse.group/jassman23/32/8238_2.png) [@JassMan23](https://klipper.discourse.group/u/JassMan23)\ **Post date:** [December 1, 2023, 11:33am UTC](https://klipper.discourse.group/t/ender-3-lost-communication-with-mcu-mcu/11981/4 "2023-12-01T11:33:04Z")
Might this be relevant? > [@Debian 11 (Bullseye) udev bug - No board or serial found](https://klipper.discourse.group/t/debian-11-bullseye-udev-bug-no-board-or-serial-found/10711): > > Background In recent updates, Debian Bullseye (Debian 11) introduced a [bug in udev](https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1035094) that causes the command ls /dev/serial/by-id/\* to fail, because the bug prevents the creation of this device path. As of writing this, the bug remains unfixed in the regular Debian repositories, but it is already fixed in optional Debian repositories. How to Diagnose To check if the OS is affected by the bug, run: sudo apt -y update && sudo apt -y upgrade apt-cache policy udev If the command’s output display… --- _[View the full topic](https://klipper.discourse.group/t/ender-3-lost-communication-with-mcu-mcu/11981)._