當你玩類似flashcache、multipath iscsi等辣手嘢嘅時候，理應係會見到呢啲嘢。原因好簡單，係事實呀嗎。除非你係先知，否則見到正常到爆，以下先講點避開，再講點處理。

閣下如果用緊RoundCube嚟做webmail，已經存在一個database（唔理係PostgreSQL定MySQL）。喺Upgrade、重新安裝、遷移時候，可能會面對Database唔兼容嘅問題。表面好似無咩事，但係到send mail嘅時候就出事啦，你會發覺啲身份無嗮！

HTML5 is available to play audio and video without plugin.  See W3SCHOOL for detail.   The page shows you Firefox and Opera does not support mp3/mp4 for license issue.   Don't spend time, use the dir2ogg software package to convert the mp3 to ogg format.   Then, provides them all including the traditional plugin embed tag.

The following steps should work on ubuntu 12.04 LTS or any linux using slapd 2.4.x.  Just installation commands have some different.

Do this:

sync

echo 3 > /proc/sys/vm/drop_caches

In some case, you may get a out of memory error due to memory used up even by I/O cache.  Such kind of error definitely is a bugs but this may cause your process failure.  I came across in KVM on ubuntu 12.04.

You may do this after backup or restore since these commands usually fill up I/O cache.