问题：
当使用代理访问网站时出现以下错误：
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The requested URL could not be retrieved
While trying to retrieve the URL: http://linkhelp.clients.google.com/tbproxy/lh/fixurl?
The following error was encountered:
Unable to determine IP address from host name for linkhelp.clients.google.com
The dnsserver returned:
Timeout
This means that:
The cache was not able to resolve the hostname presented in the URL.
Check if the address is correct.
Your cache administrator is root.
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解决方法：
这是由于代理服务器机器的DNS配置问题，代理服务器机器不能找到指定url的ip地址导致。检查/etc/resolv.conf文件配置是否正确，如不正确添加正确的配置信息，比如说：
nameserver ###.###.###.###
nameserver ###.###.###.###
可以配置多个DNS server。
重新启动squid服务。