Hello, I'm a new to ROS. I just rebuild the catkin_ws and I can't roscore. I tried but it can't work. Can you help me?

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Traceback (most recent call last):
  File "/usr/bin/rosversion", line 87, in <module>
    version = rosstack.get_stack_version(stack_name)
  File "/usr/lib/python2.7/dist-packages/rospkg/rospack.py", line 422, in get_stack_version
    return get_stack_version_by_dir(self.get_path(stack))
  File "/usr/lib/python2.7/dist-packages/rospkg/rospack.py", line 201, in get_path
    self._update_location_cache()
  File "/usr/lib/python2.7/dist-packages/rospkg/rospack.py", line 184, in _update_location_cache
    list_by_path(self._manifest_name, path, cache)
  File "/usr/lib/python2.7/dist-packages/rospkg/rospack.py", line 67, in list_by_path
    root = ElementTree(None, os.path.join(d, PACKAGE_FILE))
  File "/usr/lib/python2.7/xml/etree/ElementTree.py", line 611, in __init__
    self.parse(file)
  File "<string>", line 38, in parse
cElementTree.ParseError: XML or text declaration not at start of entity: line 2, column 0
Invalid <param> tag: Cannot load command parameter [rosversion]: command [rosversion roslaunch] returned with code [1]. 

Param xml is <param command="rosversion roslaunch" name="rosversion"/>
The traceback for the exception was written to the log file
No handlers could be found for logger "roslaunch"

here is my environment:

declare -x ROSLISP_PACKAGE_DIRECTORIES="/home/qingli/catkin_ws/devel/share/common-lisp"
declare -x ROS_DISTRO="kinetic"
declare -x ROS_ETC_DIR="/opt/ros/kinetic/etc/ros"
declare -x ROS_MASTER_URI="http://localhost:11311"
declare -x ROS_PACKAGE_PATH="/home/qingli/catkin_ws/src:/opt/ros/kinetic/share"
declare -x ROS_ROOT="/opt/ros/kinetic/share/ros"