由lsof列出的管道的FD列是什么意思?

Question

我使用以下命令来获取管道列表:

lsof | grep PIPE 

我想知道FD列的值是什么意思(第五个https://i.stack.imgur.com/zkjCn.png)。我认为r和w分别表示读和写，但是这些字符后面的数字是什么意思?

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我知道FD表示文件描述符，我想弄清楚的是列中显示的值的含义，如3r, 16w, 20r等

Answer 1

文件不只是作为流打开。其中一些在lsof的手册中列出:

FD    is the File Descriptor number of the file or:
           cwd  current working directory;
           Lnn  library references (AIX);
           err  FD information error (see NAME column);
           jld  jail directory (FreeBSD);
           ltx  shared library text (code and data);
           Mxx  hex memory-mapped type number xx.
           m86  DOS Merge mapped file;
           mem  memory-mapped file;
           mmap memory-mapped device;
           pd   parent directory;
           rtd  root directory;
           tr   kernel trace file (OpenBSD);
           txt  program text (code and data);
           v86  VP/ix mapped file;
      FD  is  followed  by one of these characters, describing the
      mode under which the file is open:
           r for read access;
           w for write access;
           u for read and write access;
           space if mode unknown and no lock
            character follows;
           '-' if mode unknown and lock
            character follows.
      The mode character is followed by one of these lock  charac-
      ters, describing the type of lock applied to the file:
           N for a Solaris NFS lock of unknown type;
           r for read lock on part of the file;
           R for a read lock on the entire file;
           w for a write lock on part of the file;
           W for a write lock on the entire file;
           u for a read and write lock of any length;
           U for a lock of unknown type;
           x  for an SCO OpenServer Xenix lock on part  of the
      file;
           X for an SCO OpenServer Xenix lock on  the   entire
      file;
           space if there is no lock.
      See  the  LOCKS  section  for  more  information on the lock
      information character.
      The FD column contents constitutes a single field for  pars-
      ing in post-processing scripts.

Answer 2

这是文件描述符。

更多信息:

• http://en.wikipedia.org/wiki/File_descriptor

文件描述符 (FD)是访问文件的抽象指示符。该术语通常用于POSIX操作系统。

在POSIX中，文件描述符是一个整数，特别是C类型int。有三个标准的POSIX文件描述符，对应于三个标准流，大概每个进程(也许守护进程除外)都应该期望拥有。

Answer 3

文件描述符是计算机操作系统中唯一标识打开文件的数字。它描述了数据资源，以及如何访问该资源。该字段的最大限制在内核中指定，可以更改以防止阻塞(在达到文件描述符限制的情况下)。