有人能帮帮我吗？这是我安装时的错误提示，我是初学者，请多多帮忙。
mtdk@mtdk-Inspiron-3437:~$ npm install -g bower
npm WARN checkPermissions Missing write access to /usr/local/lib/node_modules
/usr/local/lib
└─┬ bower@1.7.1
└── semver-utils@1.1.1

npm ERR! Linux 4.2.0-19-generic
npm ERR! argv "/usr/local/bin/node" "/usr/local/bin/npm" "install" "-g" "bower"
npm ERR! node v5.1.1
npm ERR! npm v3.3.12
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! at Error (native)
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! Please include the following file with any support request:
npm ERR! /home/mtdk/npm-debug.log

試試
sudo npm install -g bower

没权限，试试加上sudo：
sudo npm install -g bower

permission denied!就是没有权限的意思，可以用超级管理员执行，在ubuntu下加上sudo就可以了