FDESCFS(5) BSD File Formats Manual FDESCFS(5)NAME
fdescfs -- file-descriptor file system
SYNOPSIS
fdescfs /dev/fd fdescfs rw 0 0
DESCRIPTION
The file-descriptor file system, or fdescfs, provides access to the per-process file descriptor namespace in the global file system names-
pace. The conventional mount point is /dev/fd.
The file system's contents appear as a list of numbered files which correspond to the open files of the process reading the directory. The
files /dev/fd/0 through /dev/fd/# refer to file descriptors which can be accessed through the file system. If the file descriptor is open
and the mode the file is being opened with is a subset of the mode of the existing descriptor, the call:
fd = open("/dev/fd/0", mode);
and the call:
fd = fcntl(0, F_DUPFD, 0);
are equivalent.
Flags to the open(2) call other than O_RDONLY, O_WRONLY and O_RDWR are ignored.
Note: /dev/fd/0, /dev/fd/1 and /dev/fd/2 files are created by default when devfs alone is mounted. fdescfs creates entries for all file
descriptors opened by the process.
FILES
/dev/fd/#
EXAMPLES
To mount a fdescfs volume located on /dev/fd:
mount -t fdescfs null /dev/fd
SEE ALSO devfs(5), mount(8)HISTORY
The fdescfs file system first appeared in 4.4BSD. The fdescfs manual page first appeared in FreeBSD 2.2.
AUTHORS
The fdescfs manual page was written by Mike Pritchard <mpp@FreeBSD.org>, and was based on the manual page written by Jan-Simon Pendry.
BSD September 18, 2010 BSD
Check Out this Related Man Page
FD(4) BSD Kernel Interfaces Manual FD(4)NAME
fd, stdin, stdout, stderr -- file descriptor files
DESCRIPTION
The files /dev/fd/0 through /dev/fd/# refer to file descriptors which can be accessed through the file system. If the file descriptor is
open and the mode the file is being opened with is a subset of the mode of the existing descriptor, the call:
fd = open("/dev/fd/0", mode);
and the call:
fd = fcntl(0, F_DUPFD, 0);
are equivalent.
Opening the files /dev/stdin, /dev/stdout and /dev/stderr is equivalent to the following calls:
fd = fcntl(STDIN_FILENO, F_DUPFD, 0);
fd = fcntl(STDOUT_FILENO, F_DUPFD, 0);
fd = fcntl(STDERR_FILENO, F_DUPFD, 0);
Flags to the open(2) call other than O_RDONLY, O_WRONLY and O_RDWR are ignored.
IMPLEMENTATION NOTES
By default, /dev/fd is provided by devfs(5), which provides nodes for the first three file descriptors. Some sites may require nodes for
additional file descriptors; these can be made available by mounting fdescfs(5) on /dev/fd.
FILES
/dev/fd/#
/dev/stdin
/dev/stdout
/dev/stderr
SEE ALSO tty(4), devfs(5), fdescfs(5)BSD June 9, 1993 BSD
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