是什么原因导致错误:EACCES:权限被拒绝，访问'/usr/local/lib/node_modules'?

npm ERR! path /usr/local/lib/node_modules
npm ERR! code EACCES
npm ERR! errno -13
npm ERR! syscall access
npm ERR! Error: EACCES: permission denied, access '/usr/local/lib/node_modules'
npm ERR!  { Error: EACCES: permission denied, access '/usr/local/lib/node_modules'
npm ERR!   errno: -13,
npm ERR!   code: 'EACCES',
npm ERR!   syscall: 'access',
npm ERR!   path: '/usr/local/lib/node_modules' }
npm ERR! 
npm ERR! Please try running this command again as root/Administrator.

npm ERR! A complete log of this run can be found in:
npm ERR!     /Users/macbookmd101/.npm/_logs/2018-02-21T16_26_08_421Z-debug.log