14.04 - How can I run a local command (to run a script) on (just before) log out of a Unity session? - Ask Ubuntu
at risk of posting duplicate question:
how can run local script (as current user) when log out?
i read (and tried) among others:
- this one (marton's version), did nothing, used on simple script creating file, absolute paths script (being executable) , file.
- this one, must outdated; made me remove file command line able use system again.
- i looked this one, without succes.
i believe must doing wrong here, cannot find out blind spot.
context
looking elegant solution (workaround) this question, presumably result of bug, made script that, depending on argument, either takes snapshot of current desktop icon arrangement, or arranges icons, according last snapshot. script works fine, no candidate run background script.
the script therefore should run on logout get arrangement, run current user.
basic theory
as may or may not know , lot of unity actions implemented using dbus . big convenience dbus can perform lots of root-required actions calling appropriate methods in command-line without need of having admin account, instance shutting down system.
specifically in our case here interested in com.canonical.unity service, /com/canonical/unity/session path. can list information qdbus command. particularly we're interested in signals have requested in them.
$ qdbus com.canonical.unity /com/canonical/unity/session | grep 'signal.*requested.*' signal void com.canonical.unity.session.lockrequested() signal void com.canonical.unity.session.logoutrequested(bool have_inhibitors) signal void com.canonical.unity.session.rebootrequested(bool have_inhibitors) signal void com.canonical.unity.session.shutdownrequested(bool have_inhibitors) signal void com.canonical.unity.session.unlockrequested() these signals appear on bus when user clicks of shutdown, lock, logout, or reboot items in drop-down session menu on right side of unity's top bar. need this:
- monitor bus signals appear.
- once appear - perform action.
of course , big disclamer if user uses sudo shutdown -p now or gnome-session-quit , won't told dbus , whatever action wanted won't done.
monitoring dbus
conveniently there command that, dbus-monitor , can filter output using set of options, , perform action on using while read … done structure
bellow example of simple monitoring script.
dbus-monitor --profile "interface='com.canonical.unity.session',type=signal" | \ while read -r line; echo "$line" sleep 0.25 done what merely monitor bus signals , , echo them stdout if appear; of course echo command. run , , try clicking on each item in session menu should generate signals, , should see this:
$ ./logout_monitor.sh sig 1458319246 172587 2 /org/freedesktop/dbus org.freedesktop.dbus nameacquired sig 1458319251 213766 5496 /com/canonical/unity/session com.canonical.unity.session rebootrequested sig 1458319265 62555 5525 /com/canonical/unity/session com.canonical.unity.session logoutrequested sig 1458319271 856770 5555 /com/canonical/unity/session com.canonical.unity.session lockrequested sig 1458319273 223940 5564 /com/canonical/unity/session com.canonical.unity.session locked sig 1458319276 991413 5604 /com/canonical/unity/session com.canonical.unity.session unlockrequested sig 1458319278 3443 5606 /com/canonical/unity/session com.canonical.unity.session unlocked so have monitoring function can perform action once interrupt occurs. , address specific question trying solve , script taking snapshots of icons on desktop. there's no harm done if take snapshot each time signal occurs - doesn't have reboot or shutdown specifically. if monitor specific unity interface signals , take snapshots upon each signal's arrival, can simplify scripting.
interrupt-driven script
bellow can see interrupt-driven script monitor bus signals (ignoring first 1 ) , if have signal coming in , call interrupt function (which in case icon snapshot script you've written).
#!/bin/bash main() { arg="cow" dbus-monitor --profile "interface='com.canonical.unity.session',type=signal" | while read -r line; grep -q '.*nameacquired.*' <<< "$line" && continue # ignore first line if [ -n "$line" ];then interrupt $arg # call python snapshot script here fi done } interrupt() { echo 'old mcdonald had ' $arg ' e-i-e-i-o ' } main note: dbus relies on having gui session , since (as far know) starts unity/gnome login. older environments such blackbox , openbox, tty environments do not start dbus session, hence script puke if try launch in ~/.profile (i had 1 user tried , got trouble). start such script using unity's or gnome's startup applications program.
going beyond script
- dbus has lot of api's including python
- i prefer using
qdbusbecause it's simple, 1 usedbus-send. examples - the interrupt function can anything, other
dbusmethods. there's lot into.
trivia: i've used same method preventing shutdown if apt running
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