How can a script detect a user's idle time?

Just found a simple way to do it.

There is a program called xprintidle that does the trick

getting the idle time (in milliseconds) is as simple as

xprintidle

and to install

apt-get install xprintidle

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For sysadmins, it also works remotely

From an ssh session:

export DISPLAY=:0 && sudo -u john xprintidle

where john is the user logged into the X session on the remote machine.

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Note that some programs such as MPlayer seem to reset the counter.

That might be desirable or not depending on your application. For me I meant to use it to suspend the computer and the MPlayer exception is helpful.

There is another answer (https://askubuntu.com/a/1303464/56440) for those who want no resetting, but I haven't personally tested it

Answer from here:

In bash

w | tr -s " " | cut -d" " -f1,5 | tail -n+3

gives you a username/idletime pair for each shell. So basically you can get the idle information through the command w

Using the answer by josinalvo might work for some, but it didn't quite work so well for me as some programs seem to be regularly resetting the timer, on which xprintidle relies, unexpectedly. In addition, I also would not want a fullscreen application to reset the idle timer, at least not in my use case.

So I've strung together my own solution in a shell script which doesn't rely on the X11 Screen Saver extension. Instead it dumps all user input like mouse movement and key presses using xinput test-xi2 --root for one second and then compares it with a dump from the last second. If they are the same, the variable $t gets increased by 1 and gets reset in the other case. This is looped and when variable $t gets over the treshold in $idletime, it is printed that the user is idle.

idleloop() {
    touch /tmp/.{,last_}input
    cmd='stat --printf="%s"'
    idletime=120
    a=2
    t=0
    while true
    do
        timeout 1 xinput test-xi2 --root > /tmp/.input
        
        if [[ `eval $cmd /tmp/.input` == `eval $cmd /tmp/.last_input` ]]
        then
            let t++ # increases $t by 1
        else
            t=0     # resets $t
        fi

        mv /tmp/.{,last_}input -f

        if [ $t -ge $idletime ] && [[ $a == "2" ]]
        then
            echo "user has gone idle"
            a=1
        fi
        if [ $t -lt $idletime ] && [[ $a == "1" ]]
        then
            echo "user has come back from idle"
            a=2
        fi
    done
}

idleloop

Feel free to leave any suggestions.