公司服务器是CentOS 5的，最近在使用yum安装软件的时候报出了一下的异常
Loaded plugins: fastestmirror, security
Loading mirror speeds from cached hostfile
YumRepo Error: All mirror URLs are not using ftp, http[s] or file.
Eg. Invalid release/
removing mirrorlist with no valid mirrors: /var/cache/yum/extras/mirrorlist.txt
Cannot find a valid baseurl for repo: extras不论是install/update/clean等，都会出现以上错误。找了很久，最后终于在linuxquestions上找到了答案。
执行下面三行命令即可解决问题
echo "http://vault.centos.org/5.11/os/x86_64/" > /var/cache/yum/base/mirrorlist.txt
echo "http://vault.centos.org/5.11/extras/x86_64/" > /var/cache/yum/extras/mirrorlist.txt
echo "http://vault.centos.org/5.11/updates/x86_64/" > /var/cache/yum/updates/mirrorlist.txt其根本原因是，CentOS 5已经不再进行维护了，所以之前自带的Base源已经不可访问了，而vault.centos.org下面提供的目前最后一版的源。官方公告如下：
This directory (and version of CentOS) is depreciated.
CentOS-5 is now past EOL
You can get the last released version of centos 5.11 here:
http://vault.centos.org/5.11/
Please NOTE: this is not being maintained for security since moving to Vault.
It will have security issues, you should upgrade to a new version instead.
理论上来说，CentOS 5该更新了，奈何是公司服务器，运行的东西太多，重装的话比较麻烦，只好将就着用了。