使用pip安装PIL时出错

但我得到以下错误,我不知道这意味着什么.请有人帮帮我.

nishant@nishant-Inspiron-1545:~$pip install PIL
Requirement already satisfied (use --upgrade to upgrade): PIL in /usr/lib/python2.7/dist-packages/PIL
Cleaning up...
Exception:
Traceback (most recent call last):
File "/usr/lib/python2.7/dist-packages/pip/basecommand.py",line 104,in main
status = self.run(options,args)
File "/usr/lib/python2.7/dist-packages/pip/commands/install.py",line 265,in run
requirement_set.cleanup_files(bundle=self.bundle)
File "/usr/lib/python2.7/dist-packages/pip/req.py",line 1081,in cleanup_files
rmtree(dir)
File "/usr/lib/python2.7/dist-packages/pip/util.py",line 29,in rmtree
onerror=rmtree_errorhandler)
File "/usr/lib/python2.7/shutil.py",line 252,in rmtree
onerror(os.remove,fullname,sys.exc_info())
File "/usr/lib/python2.7/dist-packages/pip/util.py",line 46,in rmtree_errorhandler
os.chmod(path,stat.S_IWRITE)
OSError: [Errno 1] Operation not permitted: '/home/nishant/build/pip-delete-this-directory.txt'

Storing complete log in /home/nishant/.pip/pip.log
Traceback (most recent call last):
File "/usr/bin/pip",line 9,in <module>
load_entry_point('pip==1.1','console_scripts','pip-2.7')()
File "/usr/lib/python2.7/dist-packages/pip/__init__.py",line 116,in main
return command.main(args[1:],options)
File "/usr/lib/python2.7/dist-packages/pip/basecommand.py",line 141,in main
log_fp = open_logfile(log_fn,'w')
File "/usr/lib/python2.7/dist-packages/pip/basecommand.py",line 168,in open_logfile
log_fp = open(filename,mode)
IOError: [Errno 13] Permission denied: '/home/nishant/.pip/pip.log'