Check command availability

modules/post/linux/manage/xdg_open.rb

@@ -24,7 +24,10 @@ class MetasploitModule < Msf::Post
   end
 
   def run
-    print_status('Starting xdg-open...')
+    unless command_exists? 'xdg-open'
+      print_error 'xdg-open is not available'
+      return
+    end
     cmd_exec("xdg-open #{datastore['RES']} > /dev/null")
   end
 end

modules/post/linux/manage/xdg_screensaver.rb

@@ -35,6 +35,10 @@ class MetasploitModule < Msf::Post
 
     case action.name
       when 'STATUS'
+        unless command_exists? 'xdg-screensaver' # Specific to the X window system, should come preinstalled
+          print_error 'xdg-screensaver is not installed'
+          return
+        end
         output = cmd_exec('xdg-screensaver status')
         print_status output
       when 'LOCK'