ROS - Turtlebot simulator problem: the turtlebot model does not appear on Gazebo.

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hi, i'm a beginner with ROS world.

I use Ubuntu 16.04 (on virtual machine), Kinetic, gazebo 7.

When i execute roslaunch turtlebot_gazebo turtlebot_world.launch, Gazebo starts and models of the 3D world appear, but there is no turtlebot model!

The terminal give me this error:

IOError: [Errno 13] Permission denied: '/home/user/.ros/rosdep/sources.cache/index'
[spawn_turtlebot_model-3] process has died [pid 4179, exit code 1, cmd /opt/ros/kinetic/lib/gazebo_ros/spawn_model -unpause -urdf -param robot_description -model mobile_base __name:=spawn_turtlebot_model __log:=/home/user/.ros/log/62c9e862-31d6-11e8-b9a2-080027f2d824/spawn_turtlebot_model-3.log].
log file: /home/user/.ros/log/62c9e862-31d6-11e8-b9a2-080027f2d824/spawn_turtlebot_model-3*.log

I do not understand anything. How to solve?