Run script on screen lock/unlock

Question

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?

Answer 1

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.

Answer 2

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
)

Answer 3

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

Answer 4

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

Answer 5

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

Answer 6

this is what worked for me in ubuntu 16.04

dbus-monitor --session "type=signal,interface=org.gnome.ScreenSaver" | 
  while read MSG; do
    LOCK_STAT=`echo $MSG | grep boolean | awk '{print $2}'`
    if [[ "$LOCK_STAT" == "true" ]]; then
        echo "was locked"
    else
        echo "was un-locked"
    fi
  done