Installing Ember-CLI: How to give write access to Read-only file system (ubuntu)?

I am trying to install ember-cli in my vagrant box:

ubuntu@ubuntu-xenial:/vagrant$ sudo npm install -g ember-cli

All is looking good until it checks the file permissions:

WARN engine ember-cli@2.11.0: wanted: {"node":"0.12.* || ^4.5 || 6.* || 7.*"
(current: {"node":"4.2.6","npm":"3.5.2"})
npm WARN deprecated minimatch@2.0.10: Please update to minimatch 3.0.2 or higher to avoid a RegExp DoS issue
npm WARN checkPermissions Missing write access to /usr/local/lib

Then after that, a bunch of error lines are being displayed:

npm ERR! Linux 4.4.0-47-generic
npm ERR! argv "/usr/bin/nodejs" "/usr/bin/npm" "install" "-g" "ember-cli"
npm ERR! node v4.2.6
npm ERR! npm  v3.5.2
npm ERR! path /usr/local/lib
npm ERR! code EACCES
npm ERR! errno -13
npm ERR! syscall access

npm ERR! Error: EACCES: permission denied, access '/usr/local/lib'
npm ERR!     at Error (native)
npm ERR!  { [Error: EACCES: permission denied, access '/usr/local/lib']
npm ERR!   errno: -13,
npm ERR!   code: 'EACCES',
npm ERR!   syscall: 'access',
npm ERR!   path: '/usr/local/lib' }
npm ERR!
npm ERR! Please try running this command again as root/Administrator.
npm ERR! Linux 4.4.0-47-generic
npm ERR! argv "/usr/bin/nodejs" "/usr/bin/npm" "install" "-g" "ember-cli"
npm ERR! node v4.2.6
npm ERR! npm  v3.5.2
npm ERR! path npm-debug.log.2125708066
npm ERR! code ETXTBSY
npm ERR! errno -26
npm ERR! syscall rename

npm ERR! ETXTBSY: text file is busy, rename 'npm-debug.log.2125708066' -> 'npm-debug.log'
npm ERR!
npm ERR! If you need help, you may report this error at:
npm ERR!     <http://ift.tt/1NicLxs;

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

I tried searching for the fix but still out of luck. I'm planning to use ember-cli together w/ Rails and used the Vagrantfile here: http://ift.tt/1jCcAjF

Do you have any suggestions on how to fix this? I really think I am missing something here.