Ionic2 "Failed to copy '/node_modules/ionicons/dist/fonts/ionicons.ttf' to '/www/assets/fonts/ionicons.ttf'

when i do ionic server
keep showing message that
"Failed to copy ‘/node_modules/ionicons/dist/fonts/ionicons.ttf’ to ‘/www/assets/fonts/ionicons.ttf’ "
{ Error: EACCES: permission denied, open /www/assets/fonts/ionicons.ttf’
errno: -13,
code: ‘EACCES’,
syscall: ‘open’,
path: ‘/www/assets/fonts/ionicons.ttf’ }

i don’t know why it keeps showing these message.

if i delete all files in folder “/www/assets/fonts/”,
failed messages do not show.

However, when i try to do it again without delete files, messages show again.

i check the hooks/copy-fonts.js

var copyfiles = require(‘copyfiles’);
module.exports = function (context) {
() => { });

but it still not well.

please help me to solve this problem.