memcached添加日志输出
引子：qa的memcached总是隔一段时间挂掉，导致qa进不去。决定查一下原因，于是添加日志输出，等下次出错便于查阅、定位问题。
memcache默认没有日志输出。如果想把memecache服务日志保存到日志文件中，需要在启动参数中进行配置。
安装memache后，可以通过-h来查看支持的参数，其中关于日志输出的有以下三个：
-v verbose (print errors/warnings while in event loop) #代表打印普通的错误或者警告类型的日志信息 -vv very verbose (also print client commands/reponses) #打印的日志更详细，除了错误和警告，还包含了客户端命令和server端的响应信息 -vvv extremely verbose (also print internal state transitions) #最详尽的，甚至包含了内部的状态信息打印
根据需要选择相应的参数即可，这里选择-vv。由于需要将日志保存到文件而不是打印在控制台上，所以需要对-vv的输出进行数据流重定向。
修改memecache的脚本为：
killall memcached ; memcached -d start -m 128 -p 11211 -u root -vv >> /data/logs/mem.log.`date +%Y%m%d` 2>&1
标蓝部分是修改部分。
>> 追加形式写入日志文件中 (>表示覆盖)
/data/logs/mem.log.`date +%Y%m%d`为日志文件的名字。以年月日作为后缀来区分，无法进行日志切分(待研究和总结)，只有重启的时候才会创建新的日志文件。
2>&1 将错误信息也一同写入日志文件中（详情参考 shell输入/输出重定向）
重启memcache， 相应目录便生成日志文件。
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