This is the method I followed to add the screenlock function to PicarOS Diego 2015. Since PicarOS uses LXDE, I could find my way to do it.
1. Replacing the Screensaver:
a- Replace MateScreensaver with Xscreensaver (I used Synaptic for adding Xscreensaver).
b- Make a file called “Screensaver.desktop” with Leafpad,
add this as its content:
c- Set its permissions and make it executable (With right click / properties).
d- Save the file as root in: /etc/xdg/autostart/ (I used PCManFm as root)
e- Open the Startmenu (the cat footprint), go to Preferences /
Desktop Session Settings, and tick “Screensaver” in the list of
the tab “Automatically Started Applications”.
2. Making a Screenlock file:
a- As root, go to /usr/share/applications and make sure you have
the Screenlock.desktop file. If not, make it and add this as its
Comment=Lock your screen
b- Set its permissions and make it executable.
3. Adding Screenlock to the panel:
a- Right click on the panel and choose “panel settings”
b- Choose the tab “Panel Applets”, find the last “Application
Launch Bar” from the currently loaded plugins list. Then press the
c- You must see in the panel to your left the
button “Shutdown.” In the list of installed applications to your right, open
“Accessories” and look for Screenlock”.