引子：qa的memcached總是隔一段時間掛掉，導致qa進不去。決定查一下原因，於是添加日誌輸出，等下次出錯便於查閱、定位問題。
memcache默認沒有日誌輸出。如果想把memecache服務日誌保存到日誌文件中，需要在啓動參數中進行配置。
安裝memache後，可以通過-h來查看支持的參數，其中關於日誌輸出的有以下三個：
-v verbose (print errors/warnings while in event loop) #代表打印普通的錯誤或者警告類型的日誌信息 -vv very verbose (also print client commands/reponses) #打印的日誌更詳細，除了錯誤和警告，還包含了客戶端命令和server端的響應信息 -vvv extremely verbose (also print internal state transitions) #最詳盡的，甚至包含了內部的狀態信息打印
根據需要選擇相應的參數即可，這裏選擇-vv。由於需要將日誌保存到文件而不是打印在控制檯上，所以需要對-vv的輸出進行數據流重定向。
修改memecache的腳本爲：
killall memcached ; memcached -d start -m 128 -p 11211 -u root -vv >> /data/logs/mem.log.`date +%Y%m%d` 2>&1
標藍部分是修改部分。
>> 追加形式寫入日誌文件中 (>表示覆蓋)
/data/logs/mem.log.`date +%Y%m%d`爲日誌文件的名字。以年月日作爲後綴來區分，無法進行日誌切分(待研究和總結)，只有重啓的時候纔會創建新的日誌文件。
2>&1 將錯誤信息也一同寫入日誌文件中（詳情參考 shell輸入/輸出重定向）
重啓memcache， 相應目錄便生成日誌文件。
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