problem when using the command rospack depends1

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I used the command rospack depends1 beginner_tutorials ,but I can't get the result.

File "/usr/lib/pymodules/python2.7/rosdep2/rospack.py", line 58, in init_rospack_interface lookup = _get_default_RosdepLookup(Options()) File "/usr/lib/pymodules/python2.7/rosdep2/main.py", line 117, in _get_default_RosdepLookup verbose=options.verbose) File "/usr/lib/pymodules/python2.7/rosdep2/sources_list.py", line 567, in create_default sources = load_cached_sources_list(sources_cache_dir=sources_cache_dir, verbose=verbose) File "/usr/lib/pymodules/python2.7/rosdep2/sources_list.py", line 471, in load_cached_sources_list with open(cache_index, 'r') as f: IOError: [Errno 13] Permission denied: '/home/kevin/.ros/rosdep/sources.cache/index' Traceback (most recent call last): File "/usr/lib/pymodules/python2.7/rosdep2/rospack.py", line 58, in init_rospack_interface lookup = _get_default_RosdepLookup(Options()) File "/usr/lib/pymodules/python2.7/rosdep2/main.py", line 117, in _get_default_RosdepLookup verbose=options.verbose) File "/usr/lib/pymodules/python2.7/rosdep2/sources_list.py", line 567, in create_default sources = load_cached_sources_list(sources_cache_dir=sources_cache_dir, verbose=verbose) File "/usr/lib/pymodules/python2.7/rosdep2/sources_list.py", line 471, in load_cached_sources_list with open(cache_index, 'r') as f: IOError: [Errno 13] Permission denied: '/home/kevin/.ros/rosdep/sources.cache/index' [rospack] Error: could not call python function 'rosdep2.rospack.init_rospack_interface' f