workaround for idle monitors not sleeping in COSMIC

readme.txt

Personal workaround for https://github.com/pop-os/cosmic-greeter/issues/19 , where using an HDMI monitor as part of a dual monitor setup prevents either monitor from sleeping.

When screen is locked (explicitly or from idleness), disable second (HDMI) monitor. Re-enable monitor on screen unlock.


Notes:

watchlock.sh runs under zsh. It could certainly be rewritten to run under bash if desired; the only tricky part to get correct is the glob expansion for the lock file.

In watchlock.sh, the ID for my HDMI monitor is hardcoded (HDMI-A-3).

watchlock.sh will not trigger on logout/login. See comments in the script about why. Since I almost never log out from this system, that's OK for this workaround.

watchlock.service should be placed in the ~/.config/systemd/user directory.

If watchlock.sh is not in a PATH directory (as seen by systemd user services), then watchlock.sh needs to use a full absolute path for the value of ExecStart.

Enable and start the service with:
  systemctl enable watchlock --user
  systemctl start watchlock --user

watchlock.service

[Unit]
Description=Sleep second monitor during lock

[Service]
ExecStart=watchlock.sh
Restart=on-failure
RestartSec=3

[Install]
WantedBy=graphical-session.target

watchlock.sh

#!/usr/bin/env zsh

setopt extendedglob

screenlock=

while true
do
  old_screenlock=$screenlock
  screenlock=false
  if [[ -n $XDG_RUNTIME_DIR/cosmic-greeter-*.lock(#qN) ]]
  then
    screenlock=true
  # This else clause (to handle logout) doesn't work because when logged out,
  # cosmic-randr fails with "Error: WaylandConnection(NoCompositor)".
#  else
#    if loginctl show-user cosmic-greeter &> /dev/null
#    then
#      screenlock=true
#    fi
  fi
  if [[ $old_screenlock != $screenlock ]]
  then
    if [[ $screenlock == true ]]
    then
      echo "watchlock: disabling second monitor"
      cosmic-randr disable HDMI-A-3
    else
      echo "watchlock: enabling second monitor"
      cosmic-randr enable HDMI-A-3
    fi
  fi
  sleep 2
done