the missing knowledge base: how to fix mac os x prohibitory sign error during boot up
蘋果速成班：如果修復 Mac OS X 開機時所出現的禁止符號
According Apple knowledge base article, you may fix it by resetting NVRAM and PRAM or even reinstall your Mac.
I tried all these methods, none of them can fix the problem. I even reinstalled my Mac in different ways for 4 times within 24 hours. @.@
So how to fix it?
Before you going on the steps, answer this question, "have you installed and removed Norton Antivirus for Mac before". If your answer is No. Sorry, you get into a wrong place. Try the steps in Apple knowledge base article or find a technician.
If you said yes, congratulation, you will fix the ignoring problem within 10 minutes.
Reason
So First of all, why will this happen?
According to a Symantec employee answer on Norton Users Discussion Forum, Snow Leopard changed some system file paths. The NAV uninstaller haven't remove all the related files. With those should-be-trashed files still exist, the big tiger just simply cannot run through the boot up process. (So Symantec, why don't you just update the uninstall through LiveUpdate?)
Solution
Boot your Mac into safe mode. Download a script provided by that Symantec employee. Extract it and run the command line script. You are required to have an administrative account with non-empty password. Follow the screen instructions and let the script remove all NAV-related files. After that, everything resumed and the big tiger can running smoothly.
Anyway, I won't install NAV anymore. It is not really useful (it couldn't fix the virus when I plugged my friend's USB drive, luckily the virus only affect Windows platform), but causing many problems (such as like this one which have disturb me for 24 hours).
Maybe just like what Apple says, the antivirus software is unnecessary for Mac OS X. :P
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按蘋果知識庫文章的指示，你可以通過重置 NVRAM 和 PRAM 來解決問題，重新安裝 Mac OS X 也是一個方法。
這些方法我全試過了，我甚至在24小時內試了四種不同的重裝 Mac OS X 的方法，但問題依舊。
那怎麼辦？
在你繼續看解決方法前，先回答一條問題：「你有否安裝後再剛除了 Norton Antivirus for Mac？」如你回答沒有，很抱歉，你來錯地方了。按蘋果知識庫文章的指示又或者找個技術員幫幫你吧。
如果你的確安裝過 NAV for Mac，恭喜你，問題將會於10分鐘內被解決！
原因
歸根究底，到底是什麼導致那個禁示符號的出現？
根據 Norton Users Discussion Forum 上一位自稱為Symantec員工的回答，Snow Leopard 修改了一些系統檔案的路徑。這導致刪除 NAV 時有些檔案移除不了。就是這些被遺漏的檔案，令啟動程序出現問題。（幹麼 Symantec 不經 LiveUpdate 更新那個刪除程式呢？）
解決方案
先以安全模式啟動你的 Mac，再下載那位 Symantec 員工所製作的小工具。解壓後執行當中的指令檔。你需要一個有設置密碼的系統管理員帳戶才能順利執行指令，按畫面指示，選擇移除所有 NAV 相關的檔案。完全後重新啟動即可。
我想我不會再安裝 NAV for Mac 的了，它效用不大（曾試過清理不了 USB 記憶棒中的病毒，還好那病毒只針對 Windows 平台），但卻問題多多（像今次的問題就煩了我一整天）。
也許像 Apple 的官方答案一樣，Mac OS X 不裝防毒程式暫時也不會構成什麼大問題的吧。 :P
