Mac OS X で npm install 時に権限まわりでエラーが出たときの解決方法

環境: MacOSX Yosemite 10.10.3

npm install gulp

で以下のエラー

npm WARN package.json blogtest@1.0.0 No description
npm WARN package.json blogtest@1.0.0 No repository field.
npm WARN package.json blogtest@1.0.0 No README data
npm WARN locking Error: EACCES, open '/Users/username/.npm/_locks/gulp-9990ecbe64c4571f.lock'
npm WARN locking     at Error (native)
npm WARN locking  /Users/username/.npm/_locks/gulp-9990ecbe64c4571f.lock failed { [Error: EACCES, open '/Users/username/.npm/_locks/gulp-9990ecbe64c4571f.lock']
npm WARN locking   errno: -13,
npm WARN locking   code: 'EACCES',
npm WARN locking   path: '/Users/username/.npm/_locks/gulp-9990ecbe64c4571f.lock' }
npm ERR! Darwin 14.3.0
npm ERR! argv "node" "/usr/local/bin/npm" "install" "gulp"
npm ERR! node v0.12.2
npm ERR! npm  v2.7.5

npm ERR! Attempt to unlock /Users/username/work/practice/20150505/blogtest/node_modules/gulp, which hasn't been locked
npm ERR!
npm ERR! If you need help, you may report this error at:
npm ERR!     <https://github.com/npm/npm/issues>

npm ERR! Please include the following file with any support request:
npm ERR!     /Users/username/work/practice/20150505/blogtest/npm-debug.log

/Users/username/.npm/_locks 以下の権限がrootになっているのでエラーになっている模様

sudo chown -R `whoami` ~/.npm/_locks/

で権限変更するとうまくいく