Define custom shortcuts in Lubuntu - lightblueseas/linuxstuff GitHub Wiki
You can define custom or alternative shortcuts in lubuntu.
For do this you have to extend the file ~/.config/openbox/lubuntu-rc.xml
Note: make a backup from this config file before you make any changes.
For create a shortcut for call the shutdown dialog with the shortcut "Window Logo + End".
- 
Open xml-file ~/.config/openbox/lubuntu-rc.xml 
- 
Find the keyboard area to set keybind element. 
- 
Add following code as last entry in the keyboard area: 
   <!-- Alternative for shutdown dialog on "Window Logo + End"-->
   <keybind key="W-End">
     <action name="Execute">
       <command>lxsession-default quit</command>
     </action>
   </keybind>- 
Save the xml-file ~/.config/openbox/lubuntu-rc.xml 
- 
Open a terminal and call 
openbox --reconfigureif this didnt help you can alternative logout and login.
- Now you can use defined custom shortcut
For create a shortcut for lock your screen with the shortcut "Window Logo + L".
- 
Open xml-file ~/.config/openbox/lubuntu-rc.xml 
- 
Find the keyboard area to set keybind element. 
- 
Add following code as last entry in the keyboard area: 
    <!-- Alternative for lock the screen on "Window Logo + L"-->
    <keybind key="W-l">
      <action name="Execute">
        <command>lxsession-default lock</command>
      </action>
    </keybind>- 
Save the xml-file ~/.config/openbox/lubuntu-rc.xml 
- 
Open a terminal and call 
openbox --reconfigureif this didnt help you can alternative logout and login.
- Now you can use defined custom shortcut