> For the complete documentation index, see [llms.txt](https://applezulab.netdpi.net/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://applezulab.netdpi.net/02-linux-xi-tong-cao-zuo/umask.md).

# umask()

一般系統預設開啟檔案的存取權限會是 0666 , 目錄是 0777

然而 umask 可以更改建立檔案的預設權限

ex. umask 0022

則當我們建立一個檔案，如

$ touch hi $ ls -l hi

則可以觀察到，權限會是 0666 - 0022 = 0644

所以有些程式如果不想有 umask，在設計時就會在一開始 umask(0)，清除本來系統中的 umask 設定。


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