虚拟机ubuntu安装express出错

npm ERR! Error: EROFS, symlink '../express/bin/express'
npm ERR! If you need help, you may report this log at:
npm ERR! <http://github.com/isaacs/npm/issues>
npm ERR! or email it to:
npm ERR! <npm-[@googlegroups](/user/googlegroups).com>

npm ERR! System Linux 3.8.0-19-generic
npm ERR! command "/usr/local/bin/node" "/usr/local/bin/npm" "install"
npm ERR! cwd /home/www/nodejs/demo
npm ERR! node -v v0.10.15
npm ERR! npm -v 1.3.5
npm ERR! path ../express/bin/express
npm ERR! code EROFS
npm ERR! errno 56