安装MAC OS X El Capitan后出现错误

我的Mac上安装了NodeJS。

$ node -v
v4.2.1

我正在尝试安装凉亭。结果如下：

npm ERR! Darwin 15.0.0
npm ERR! argv "/usr/local/bin/node" "/usr/local/bin/npm" "install" "-g" "bower"
npm ERR! node v4.2.1
npm ERR! npm  v2.14.7
npm ERR! path /usr/local/lib/node_modules/bower
npm ERR! code EACCES
npm ERR! errno -13
npm ERR! syscall rmdir

npm ERR! Error: EACCES: permission denied, rmdir '/usr/local/lib/node_modules/bower'
npm ERR!     at Error (native)
npm ERR!  { [Error: EACCES: permission denied, rmdir '/usr/local/lib/node_modules/bower']
npm ERR!   errno: -13,
npm ERR!   code: 'EACCES',
npm ERR!   syscall: 'rmdir',
npm ERR!   path: '/usr/local/lib/node_modules/bower' }
npm ERR!
npm ERR! Please try running this command again as root/Administrator.
npm ERR! error rolling back Error: EACCES: permission denied, rmdir '/usr/local/lib/node_modules/bower'
npm ERR! error rolling back     at Error (native)
npm ERR! error rolling back  { [Error: EACCES: permission denied, rmdir '/usr/local/lib/node_modules/bower']
npm ERR! error rolling back   errno: -13,
npm ERR! error rolling back   code: 'EACCES',
npm ERR! error rolling back   syscall: 'rmdir',
npm ERR! error rolling back   path: '/usr/local/lib/node_modules/bower' }

npm ERR! Please include the following file with any support request:
npm ERR!     /Users/Kevin/Sites/npm-debug.log

我试着做：

$ sudo chown -R $(whoami) ~/.npm
chown: /Users/Kevin/.npm/_locks: Operation not permitted
chown: /Users/Kevin/.npm/bower/1.6.3/package/package.json: Operation not permitted
chown: /Users/Kevin/.npm/bower/1.6.3/package: Operation not permitted
chown: /Users/Kevin/.npm/bower/1.6.3/package.tgz: Operation not permitted
chown: /Users/Kevin/.npm/bower/1.6.3: Operation not permitted
chown: /Users/Kevin/.npm/bower: Operation not permitted
chown: /Users/Kevin/.npm/n: Operation not permitted

看来我完全没有权限。我什么都无法安装。

我该如何解决？