Create launcher for save_map

edit

I wonder how is possible to create a launcher for saving a map after gmapping using a launcher. In my case I create two simultaneous maps. I created a launcher but it is giving the following error:

[map_server-1] process has died [pid 21969, exit code 255, cmd /opt/ros/kinetic/lib/map_server/map_server /home/christen/catkin_ws/src/map_filtering __name:=map_server __log:=/home/christen/.ros/log/058df484-23a4-11e9-b2e5-08002707828c/map_server-1.log].
log file: /home/christen/.ros/log/058df484-23a4-11e9-b2e5-08002707828c/map_server-1*.log
[map_server_2-2] process has died [pid 21970, exit code 255, cmd /opt/ros/kinetic/lib/map_server/map_server /home/christen/catkin_ws/src/map_filtering __name:=map_server_2 __log:=/home/christen/.ros/log/058df484-23a4-11e9-b2e5-08002707828c/map_server_2-2.log].
log file: /home/christen/.ros/log/058df484-23a4-11e9-b2e5-08002707828c/map_server_2-2*.log

The launcher I created is the following:

<launch>
  <node name="map_server" pkg="map_server" type="map_server" args="$(find map_filtering)">
    <param name="map" value="/map"/>
  </node>
  <node name="map_server_2" pkg="map_server" type="map_server" args="$(find map_filtering)">
    <param name="map" value="/map_2"/>
  </node>
</launch>

with args I understand the directory where the maps are going to be saved, maybe I am wrong.

Do you spot the error? How do I add an argument to save the map with a customized name?

Thanks for your time :)