项目使用composer进行包管理，但是进行包升级时报以下错误，该怎么解决？

 ubuntu@ubuntu-VGN-SR13-B:~/nginx/coolwifi$ composer selfupdate
PHP Fatal error:  Uncaught exception 'PharException' with message 'phar "/usr/local/bin/composer" has a broken signature' in /usr/local/bin/composer:13
Stack trace:
#0 /usr/local/bin/composer(13): Phar::mapPhar('composer.phar')
#1 {main}
  thrown in /usr/local/bin/composer on line 13

解决：删掉/usr/local/bin/composer后，重新下载composer.phar复制进去添加执行权限后正常