bash - "rw-"文件模式中的第三个符号是什么意思？

Question

我无法理解 ls 关于具有 rw- 模式的文件的手册。这是引述:

1. If r, the file is readable; if -, it is not readable.

2. If w, the file is writable; if -, it is not writable.

3. The first of the following that applies:

   S If in the owner permissions, the file is not executable and set-user-ID mode is set. If in the group permissions, the file is not executable and set-group-ID mode is set.

   s If in the owner permissions, the file is executable and set-user-ID mode is set. If in the group permissions, the file is executable and setgroup-ID mode is set.

   x The file is executable or the directory is searchable.

   - The file is neither readable, writable, executable, nor set-user-ID nor set-group-ID mode, nor sticky.

特别是，两个粗体部分似乎相互矛盾:根据第一个，因为模式以 r 开头，文件是可读的，但根据最后一个，文件不可可读。但是，显然情况并非如此。

那么，第三部分关于文件“既不可读，也不可写...”是什么意思？

Answer 1

您的 ls 手册页不是标准的。 POSIX standard man page for ls 没有那样说。以下是相关摘录:

Each field shall have three character positions:

1. If 'r' , the file is readable; if '-' , the file is not readable.

2. If 'w' , the file is writable; if '-' , the file is not writable.

3. The first of the following that applies:

   S

   If in < owner permissions>, the file is not executable and set-user-ID mode is set. If in < group permissions>, the file is not executable and set-group-ID mode is set.

   s

   If in < owner permissions>, the file is executable and set-user-ID mode is set. If in < group permissions>, the file is executable and set-group-ID mode is set.

   T

   If in < other permissions> and the file is a directory, search permission is not granted to others, and the restricted deletion flag is set.

   t

   If in < other permissions> and the file is a directory, search permission is granted to others, and the restricted deletion flag is set.

   x

   The file is executable or the directory is searchable.

   -

   None of the attributes of 'S' , 's' , 'T' , 't' , or 'x' applies.

我认为这更有意义。

类型未在权限位中表示 - 您只查看 ls(1) 报告的内容，而不是它的存储方式。传统上，模式和类型一起使用 32 位，但这取决于文件系统，现在很多文件系统都是 64 位的。权限在 inode 中只有 9 位。

查看 man 2 stat 并搜索 st_mode。 ls(1) 可能使用的是低级 C 例程。在某些平台上，它还可以作为命令行程序使用 man 1 stat。