rosrun map_server map_saver keeps on waiting does not generate map.

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hello, i am Build a Map Using Logged Data. I am following the procedure as explained in the ROS Tutorial click to go.

Here are the steps i am following:-

1. $ roscore
2. $ rosparam set use_sim_time true
3. $ rosrun gmapping slam_gmapping scan:=base_scan
4. $ rosbag play --clock mylaserdata.bag

everything goes fine till here, but at the 5th step while executing following command...

5. $ rosrun map_server map_saver

This displays following message:-

[INFO] [1413492118,722337006]: Waiting for the map

and then map_server keeps on waiting but neither it stops nor save the map, i am wondering why this is happening i can't figure out the problem since there are not any error, the size of my bag file is 5MB.

please help, thanks in advance.