mjhjmtu

I'd like to run a screen if the Gnome session is locked and unlocked. Is there a way that I can intercept this and perform certain actions when the desktop is locked or unlocked?

Gnome-screensaver emits some signals on dbus when something happens.

Here the documentation (with some examples).

You could write a scripts that runs:

dbus-monitor --session "type='signal',interface='org.gnome.ScreenSaver'"

and that does what you need anytime dbus-monitor prints a line about the screen being locked/unlocked.

Here a bash command to do what you need:

dbus-monitor --session "type='signal',interface='org.gnome.ScreenSaver'" |
 while read x; do
 case "$x" in 
 *"boolean true"*) echo SCREEN_LOCKED;;
 *"boolean false"*) echo SCREEN_UNLOCKED;; 
 esac
 done

Just replace echo SCREEN_LOCKED and echo SCREEN_UNLOCKED with what you need.

In ubuntu 14.04 the DBus event for screen lock unlock has changed and the new script for binding to screen lock and unlock events looks like the following

dbus-monitor --session "type='signal',interface='com.ubuntu.Upstart0_6'" | 
(
 while true; do
 read X
 if echo $X | grep "desktop-lock" &> /dev/null; then
 SCREEN_LOCKED;
 elif echo $X | grep "desktop-unlock" &> /dev/null; then
 SCREEN_UNLOCKED;
 fi
 done
)

Ubuntu 16.04: ozma’s solution did not work for me, however this one did:

dbus-monitor --session "type=signal,interface=com.canonical.Unity.Session,member=Unlocked" | 
 while read MSG; do
 LOCK_STAT=`echo $MSG | awk 'print $NF'`
 if [[ "$LOCK_STAT" == "member=Unlocked" ]]; then
 echo "was unlocked"
 fi
 done

Expanding on already given answer.

If you try to run a script from inside a screen or tmux session, you'll need to find the correct $DBUS_SESSION_BUS_ADDRESS first and pass it as an argument for dbus-monitor instead of --session. Also if you're running it as a daemon you should make sure only one instance is running at a time (e.g. with a lock file) and that the script cleans up after itself with trap. The following example will work as a daemon in most current Gnome environments (tested on Ubuntu GNOME 16.04):

#!/bin/bash
set -o nounset # good practice, exit if unset variable used

pidfile=/tmp/lastauth.pid # lock file path
logfile=/tmp/lastauth.log # log file path

cleanup() # when cleaning up:
 rm -f $pidfile # * remove the lock file
 trap - INT TERM EXIT # * reset kernel signal catching
 exit # * stop the daemon


log() # simple logging format example
 echo $(date +%Y-%m-%d %X) -- $USER -- "$@" >> $logfile


if [ -e "$pidfile" ]; then # if lock file exists, exit
 log $0 already running...
 exit
fi

trap cleanup INT TERM EXIT # call cleanup() if e.g. killed

log daemon started...

echo $$ > $pidfile # create lock file with own PID inside

# usually `dbus-daemon` address can be guessed (`-s` returns 1st PID found)
export $(grep -z DBUS_SESSION_BUS_ADDRESS /proc/$(pidof -s dbus-daemon)/environ)

expr='type=signal,interface=org.gnome.ScreenSaver' # DBus watch expression here

dbus-monitor --address $DBUS_SESSION_BUS_ADDRESS "$expr" | 
 while read line; do
 case "$line" in
 *"boolean true"*) log session locked;;
 *"boolean false"*) log session unlocked;;
 esac
 done

cleanup # let's not leave orphaned lock file when the loop ends (e.g. dbus dies)

If this doesn't work for you, it's probably because:

1. you don't use Gnome - check other answers for better DBus watch expression


2. you run multiple DBus lines - check details on how to make PID finding deterministic

If you're on Kubuntu or using KDE / Plasma as your Desktop Environment, you have to listen for the interface org.freedesktop.ScreenSaver, so the script for listening to that event would look like this:

dbus-monitor --session "type='signal',interface='org.freedesktop.ScreenSaver'" |
 while read x; do
 case "$x" in 
 *"boolean true"*) echo SCREEN_LOCKED;;
 *"boolean false"*) echo SCREEN_UNLOCKED;; 
 esac
 done

Nowadays I think it's better to listen to the LockedHint rather than screensaver messages. That way you're not tied to a screensaver implementation.

Here's a simple script to do that:

gdbus monitor -y -d org.freedesktop.login1 | grep LockedHint

Gives this:

/org/freedesktop/login1/session/_32: org.freedesktop.DBus.Properties.PropertiesChanged ('org.freedesktop.login1.Session', 'LockedHint': <true>, @as )
/org/freedesktop/login1/session/_32: org.freedesktop.DBus.Properties.PropertiesChanged ('org.freedesktop.login1.Session', 'LockedHint': <false>, @as )

Where to write this code and how it will run:

dbus-monitor --session "type='signal',interface='org.gnome.ScreenSaver'" |
 while read x; do
 case "$x" in 
 *"boolean true"*) echo SCREEN_LOCKED;;
 *"boolean false"*) echo SCREEN_UNLOCKED;; 
 esac
 done