最近发现苹果电脑在休眠之后经常会出现上不去网的情况。因为在公司是使用Proxifier代理上网，Proxifier报错：

[08.15 12:24:18] Kernel log : sf\_connect\_out : QQ(15257,502): already connected
[08.15 12:24:18] Kernel log : sf\_connect\_out : Mail(15646,502): already connected
[08.15 12:24:18] Kernel log : sf\_connect\_out : QQ(15257,502): already connected
[08.15 12:24:18] Kernel log : sf\_connect\_out : QQ(15257,502): already connected
[08.15 12:24:18] Kernel log : sf\_connect\_out : QQ(15257,502): already connected
[08.15 12:24:18] Kernel log : sf\_connect\_out : sharingd(254,502): already connected

网上找了一圈，没有什么解决办法。然后想起查看系统日志，在控制台(Console.app)中看找到这些:

16/8/15 下午12:24:17.979 QQ[15257]: dnssd\_clientstub write\_all(26) failed -1/28 57 Socket is not connected
16/8/15 下午12:24:17.980 QQ[15257]: tcp\_connection\_host_start 6986 DNSServiceCreateConnection failed: -65537
16/8/15 下午12:24:18.031 QQ[15257]: dnssd\_clientstub write\_all(19) failed -1/28 57 Socket is not connected
16/8/15 下午12:24:18.032 QQ[15257]: tcp\_connection\_host_start 6987 DNSServiceCreateConnection failed: -65537
16/8/15 下午12:24:18.036 QQ[15257]: dnssd_clientstub ConnectToServer: connect()-> No of tries: 1
16/8/15 下午12:24:18.083 Mail[15646]: dnssd\_clientstub write\_all(66) failed -1/28 57 Socket is not connected
16/8/15 下午12:24:18.084 Mail[15646]: tcp\_connection\_host_start 727 DNSServiceCreateConnection failed: -65537
16/8/15 下午12:24:18.088 Mail[15646]: dnssd_clientstub ConnectToServer: connect()-> No of tries: 1
16/8/15 下午12:24:18.145 QQ[15257]: dnssd\_clientstub write\_all(20) failed -1/28 57 Socket is not connected
16/8/15 下午12:24:18.145 QQ[15257]: tcp\_connection\_host_start 6988 DNSServiceCreateConnection failed: -65537
16/8/15 下午12:24:18.311 QQ[15257]: dnssd\_clientstub write\_all(29) failed -1/28 57 Socket is not connected
16/8/15 下午12:24:18.311 QQ[15257]: tcp\_connection\_host_start 6991 DNSServiceCreateConnection failed: -65537
16/8/15 下午12:24:18.311 QQ[15257]: dnssd_clientstub ConnectToServer: connect()-> No of tries: 1

再去google，终于找到了解决办法，这是原文：

https://inderpreetsingh.com/2015/01/23/mdnsresponder-and-discoveryd-hanging-in-yosemite-cpu-spikes-at-100/

虽然她遇到的问题是CPU占用100%，不过解决方案居然相似。

她的解决方案是重启discoveryd，因为他本机没有mDNSResponder，而正相反，我没有discoveryd。

于是重启mDNSResponder后顺利上网了。

电脑相关情况：

MBP2015年初版

Mac OS Yosemite 10.10.5

解决方案：

控制台执行

sudo launchctl unload -w /System/Library/LaunchDaemons/com.apple.mDNSResponder.plist
sudo launchctl load -w /System/Library/LaunchDaemons/com.apple.mDNSResponder.plist

如果没有mDNSResponder不妨试试

sudo launchctl unload -w /System/Library/LaunchDaemons/com.apple.discoveryd.plist
sudo launchctl load -w /System/Library/LaunchDaemons/com.apple.discoveryd.plist