why i can't run my gazebo model in paused mode?

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Hello,

i have been trying to open my URDF model in Gazebo and recently i succeeded by changing the directory to the ROS workspace and by using the command below i am able to load my model in Gazebo.

samia@samia:~/catkin_ws/src/base_2links/src/launch$ roslaunch gazebo.launch

but my model appears to be collapsed due to the effect of gravity, so i want to load the simulation in the paused mode but i am facing some problems. I entered the command below in the home directory to launch an empty world and it worked.

samia@samia:~$ roslaunch gazebo_ros empty_world.launch paused:=true use_sim_time:=false gui:=true throttled:=false recording:=false debug:=true verbose:=true gui_required:=true

when i try to run my model i go to the directory of the .launch file and try to run the same command but instead of empty_world.launch i enter gazebo.launch as shown below

samia@samia:~/catkin_ws/src/base_2links/src/launch$ roslaunch gazebo_ros gazebo.launch paused:=true use_sim_time:=false gui:=true throttled:=false recording:=false debug:=true verbose:=true gui_required:=true

and get this error----> [gazebo.launch] is neither a launch file in package [gazebo_ros] nor is [gazebo_ros] a launch file name The traceback for the exception was written to the log file