Udev logging [solved]

[paulj]

I am trying to make a simple rule for udev to run configure xrandr when I plug in an HDMI monitor into my laptop. Pretty straight forward, and basically copied from elsewhere on the web. Anyway, it doesn't seem to do anything, so I decided to set up udev to give more information. Unfortunately, neither using

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udevadm --log-priority="info"

or changing the relevant line in /etc/udev/udev.conf (and rebooting) seems to send any information to /var/log/messages or /var/log/dmesg. Should I be looking somewhere else?

udev version 225-r1 (stable) and openrc (no systemd).

Many thanks!

[paulj]

Since I am not making any progress with this issue, can anyone confirm they can get logging functioning with udev, or eudev. Perhaps the time has come to move over to eudev, since I have no interest in systemd!

Many thanks!

[cboldt]

I have eudev here, but suspect the logging widgets are similar between the two packages.

I studied the man pages for udev, udevd, udevadm, and udev.conf -- the closes matches I get for your issue are

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udevadm monitor

and for the udevd daemon, setting environment variable $UDEV_LOG

I vaguely recall using `udevadm monitor` to debug a USB-attache device, probably a few years ago. It worked fine for the purpose. Other udevadm commands have been useful to find the details that udev has used to define the system and various devices. I've never changed the log level on the daemon.

The only udev-related entries in logs on my systems are for portage installing the packages, and in dmesg, "udevd[713]: starting version 3.1.5"

[paulj]

Thanks for the reply - you are right - udevadm monitor does give one level of information:

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monitor will print the received events for:
UDEV - the event which udev sends out after rule processing                                                                          
KERNEL - the kernel uevent 

KERNEL[27864.579513] change   /devices/pci0000:00/0000:00:02.0/drm/card0 (drm)
ACTION=change
DEVNAME=/dev/dri/card0
DEVPATH=/devices/pci0000:00/0000:00:02.0/drm/card0  
DEVTYPE=drm_minor                                                                  
HOTPLUG=1
MAJOR=226
MINOR=0
SEQNUM=2973
SUBSYSTEM=drm

UDEV  [27864.584369] change   /devices/pci0000:00/0000:00:02.0/drm/card0 (drm)
ACTION=change
DEVNAME=/dev/dri/card0
DEVPATH=/devices/pci0000:00/0000:00:02.0/drm/card0
DEVTYPE=drm_minor
HOTPLUG=1
ID_PATH=pci-0000:00:02.0
ID_PATH_TAG=pci-0000_00_02_0
MAJOR=226
MINOR=0
SEQNUM=2973
SUBSYSTEM=drm
TAGS=:udev-acl:
USEC_INITIALIZED=13393469

This let me know the message from udev which I want to respond to.

My rule:

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ACTION=="change", SUBSYSTEM=="drm", HOTPLUG=="1", RUN+="/usr/local/bin/hotplug.sh"

As you can see, this should trigger for the above event.

My script:

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#!/bin/bash

# Script to automatically setup HDMI monitor with xrandr on hotplug
# From: https://kdecherf.com/blog/2015/01/16/xrandrudev-hotplug-an-external-screen-no-matter-which-output-it-is/


set -o pipefail

export DISPLAY=:0.0
export XAUTHORITY=/home/paul/.Xauthority

function connect(){
    logger -t udev "HDMI Connected"
    xrandr --output HDMI1 --auto --right-of LVDS1
}
 
function disconnect(){
    logger -t udev "HDMI Disconnected"
    xrandr --output HDMI1 --off
}

xrandr | grep "HDMI connected" &> /dev/null && connect || disconnect

Pretty simple, but never run!

The script permissions:

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-rwxr-xr-x 1 root root 942 May  6 18:18 /usr/local/bin/hotplug.sh

Finally I did manage to get he logging working, but I had to take two steps:

• Modify /etc/conf.d/udev:

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  # /etc/conf.d/udev: config file for udev
  
  # Add extra command line options to udevd, use with care
  # udevd --help for possible values
  #udev_opts=""
  
  # Run udevd --debug and write output to /run/udevdebug.log
  # Should not be kept on as it fills diskspace slowly
  udev_debug="YES"
  

• Modify /etc/udev/udev.conf:

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  # see udev.conf(5) for details
  
  udev_log="debug"
  

  This gives a more comprehensive log at /run/udevdebug.log. Here is an extract of the activity around the udev startup:
  

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  Reading rules file: /lib64/udev/rules.d/95-cd-devices.rules
  Reading rules file: /lib64/udev/rules.d/95-dm-notify.rules
  Reading rules file: /lib64/udev/rules.d/95-upower-csr.rules
  Reading rules file: /lib64/udev/rules.d/95-upower-hid.rules
  Reading rules file: /lib64/udev/rules.d/95-upower-wup.rules
  Reading rules file: /lib64/udev/rules.d/97-hid2hci.rules
  Reading rules file: /lib64/udev/rules.d/99-fuse.rules
  Reading rules file: /etc/udev/rules.d/99-monitor.rules
  unknown key 'HOTPLUG' in /etc/udev/rules.d/99-monitor.rules:1
  invalid rule '/etc/udev/rules.d/99-monitor.rules:1'
  

  As you can see it doesn't like the HOTPLUG key, even though it is in the monitor output, so now I know where to work next.
  
  Here is the debug log for the event when the monitor is plugged in:

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  seq 2154 queued, 'change' 'drm'
  Validate module index
  Check if link configuration needs reloading.
  seq 2154 forked new worker [3845]
  seq 2154 running
  IMPORT builtin 'path_id' /lib64/udev/rules.d/60-drm.rules:3
  RUN 'udev-acl --action=$env{ACTION} --device=$env{DEVNAME}' /lib64/udev/rules.d/70-udev-acl.rules:74
  handling device node '/dev/dri/card0', devnum=c226:0, mode=0600, uid=0, gid=0
  preserve already existing symlink '/dev/char/226:0' to '../dri/card0'
  created db file '/run/udev/data/c226:0' for '/devices/pci0000:00/0000:00:02.0/drm/card0'
  starting 'udev-acl --action=change --device=/dev/dri/card0'
  Process 'udev-acl --action=change --device=/dev/dri/card0' succeeded.
  passed device to netlink monitor 0x55fe2bc3b1f0
  seq 2154 processed
  

  So know I know where to check for the next step once the script is valid.
  
  In case anyone else is here with the same type of issue, don't forget the /run directory is volatile. If you need to save the logfile to work on the contents, copy it somewhere else before rebooting.