Linux 的目录权限与文件权限的区别

更新日期: 2018-01-24 阅读次数: 528 分类: Linux

问题

帮朋友搭建一个 wordpress 站点,偷懒的在 root 帐号根目录下部署了。出现了神器的报错

stat() "/root/wordpress/" failed (13: Permission denied)
stat() "/root/wordpress/" failed (13: Permission denied)
stat() "/root/wordpress/index.php" failed (13: Permission denied)
"/root/wordpress/index.php" is forbidden (13: Permission denied)

页面上显示 404。这就非常诡异了,日志中显示权限有问题。即使我将 /root/wordpress/ 整个目录及子目录、文件都设置成 777 权限,也不行。还是报权限错误!

万能的 777 都不行,还能怎么办?

救赎

Google 到了一个答案

https://serverfault.com/questions/170192/nginx-php-fpm-permission-denied-error-13-in-nginx-log-configuration-mista/170263#170263

You need to ensure you have +x on all of the directories in the path leading to the site's root - so /home, /home/noisepages and /home/noisepages/www

也就是说,需要将路径中的每一个目录都加上执行权限。果然,

chmod +x /root

之后,一切都正常了。。。

然而,我完全不明白这是在干啥?

为什么,父级目录的权限会影响到子目录的访问。

冷静一下

For a directory, execute permission allows a user to access, or traverse, into (i.e. cd) and access metadata about files in the directory (the information that is listed in an ls -l).

stat 函数,是通过文件名获取到对应的文件信息。(类似,ls -l)

这样想,如果为了安全,我将一个用户根目录针对另一个用户去掉了执行权限。那么理论上,其子目录的信息,都禁止其访问。除非他能通过 sudo cd 进去。

那么,上面的问题就很好理解了。想通过文件/目录的绝对路径调用 stat 函数,获得文件信息,逻辑上是不能被允许的。那么报错就符合逻辑了。

The way you access a file matters. For example, if you have execute permissions on /foo/bar but not on /foo, but your current directory is /foo/bar, you can access files in /foo/bar through a relative path but not through an absolute path. You can't change to /foo/bar in this scenario; a more privileged process has presumably done cd /foo/bar before going unprivileged. If a file has multiple hard links, the path you use to access it determines your access constraints.

下次如何快速定位问题

如果想快速查看绝对路径中的每一个目录的权限及所有者,可以使用 namei 命令

$ namei -mo ~/test/wordpress
f: /home/zhongwei/test/wordpress
 drwxr-xr-x root     root     /
 drwxr-xr-x root     root     home
 drwx------ zhongwei zhongwei zhongwei
 drwxr-xr-x zhongwei zhongwei test
 drwxr-xr-x zhongwei zhongwei wordpress

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