No /clock topic being published when running map_server map_saver

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Hello,

I have been following the ROS gmapping tutorial, How to Build a Map Using Logged Data, and have run into a problem where the sim clock is not being published when I try to save a map from a bag file.

• I set the ues_sim_time parameter to true.
• Am running gmapping slam_gmapping.
• The bag file succesfully played back using: rosbag play --clock myBagFile.bag
• but after processing the bag file, I use rosrun map_server map_saver -f myMap and I get the message: Waiting for the map

The /Clock topic is not being published. Isn't map_server map_saver supposed to publish the /clock topic?

From roswtf:

WARNING The following node subscriptions are unconnected: * /slam_gmapping: * /tf_static * /clock * /scan * /rostopic_5755_1528131980494: * /clock * /map_saver: * /clock

WARNING No tf messages

Found 1 error(s).

ERROR /use_simtime is set but no publisher of /clock is present