Libnotify from udev
I've been searching for a long time, and I finally figured out how to generate a libnotify event from a udev rule without hardcoding the username into the rule or script. The answer is actually pretty simple, and I'm very surprised I couldn't find the answer on any wiki or forum.
There was this ArchWiki entry which is no help at all. The author seemed to think you could insert a $USER variable into here "once you understand the example". What? If your generic example contains hardcoded elements it's a horrible example! /vent
Moving on.
I thought I might be able to use this blog's tutorial on how to start systemd services from udev for my purposes, but that quickly got very complicated and confusing. It took me an embarrasingly long time to realize this approach still requires a hardcoded username implemented somewhere. Womp womp.
I got the basic framework for my solution with the help of hackaday. They still hardcode the user, but thinking about what they did here caused me to arrive at the solution.
In their for loop, they iterate through every instance of their notification daemon. While I was cleaning up their useless use of grep, I wondered what that for loop actually accomplishes; are they expecting to have more than one instance of their notification daemon running? That doesn't make sense. My notification daemon of choice, dunst, doesn't even let you run it more than once per user. At which point it occurred to me, if this script is run as root, I can repurpose this for loop to iterate the search for a notification daemon through logged in users! I had to look up the who command as I had never seen it before, and from here the problem is solved. I no longer need to figure out which users to run notify-send as, I run it for every logged in user. Which makes sense for hardware events- all logged in users should be getting these notifications.
Now if only I could find a way to not hardcode the notification daemon.
/usr/local/bin/power_notify
#!/bin/sh # Display a notification for each logged in user user_notify() { users=$(who | awk '{print $1}') for user in $users; do # find DBUS session bus pid=$(pgrep -u $user dunst) export DBUS_SESSION_BUS_ADDRESS=$(sed -z -e '/DBUS_SESSION_BUS_ADDRESS/!d' \ -e 's/DBUS_SESSION_BUS_ADDRESS=//' /proc/$pid/environ) su -c - $user "$@" done } # udev 99-lowbat.rules case "$1" in "low") user_notify "notify-send -u normal 'Low Battery'" ;; "critical") user_notify "notify-send -u critical 'Low Battery' 'Find power soon!'" ;; "suspend") user_notify "notify-send -u critical 'Suspend Imminent' 'The system is going down in two minutes!'" sleep 120 systemctl suspend ;; "hibernate") echo "not implemented" ;; esac
/etc/udev/rules.d/99-lowbat.rules
SUBSYSTEM=="power_supply", KERNEL=="BAT0", ATTR{capacity}=="2[05]", ATTR{status}=="Discharging", RUN+="/usr/local/bin/power_notify low" SUBSYSTEM=="power_supply", KERNEL=="BAT0", ATTR{capacity}=="1[05]", ATTR{status}=="Discharging", RUN+="/usr/local/bin/power_notify critical" SUBSYSTEM=="power_supply", KERNEL=="BAT0", ATTR{capacity}=="[0-9]", ATTR{status}=="Discharging", RUN+="/usr/local/bin/power_notify suspend"
