How can I lock screen on lxde

You should be able to bind the screensaver lock command to CTRL+ALT+L by editing your Lubuntu keyboard & mouse configuration file

Add the following to ~/.config/openbox/lubuntu-rc.xml

<keybind key="C-A-L">      
  <action name="Execute">        
    <command>xscreensaver-command -lock</command>      
  </action>    
</keybind>

This should be located inbetween the XML tags

<keyboard>
...
</keyboard

enter image description here

Logout and login for the changes to take effect.

I would elaborate/combine some of the answers. First (in a terminal) start your editor:

vi ~/.config/openbox/lubuntu-rc.xml

Then search for the mentioned faulty code:

<keybind key="C-A-L">      
  <action name="Execute">        
    <command>xscreensaver-command -lock</command>      
  </action>    
</keybind>

and change it to use the dm-tool:

<keybind key="C-A-L">      
  <action name="Execute">        
    <command>dm-tool lock</command>      
  </action>    
</keybind>

Then add a section, so the Windows+L combination works too:

<keybind key="W-L">
  <action name="Execute">        
    <command>dm-tool lock</command>      
  </action>    
</keybind>

Finally, finish the editor (saving the file) and activate it:

openbox --reconfigure

Good luck and thanks for all the answers found here...

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