FD(4) | Device Drivers 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.

These devices may not be opened by processes which are tainted as a result of setuid or setgid behaviours, as documented in issetugid(2). In those cases, an error return will occur with errno set to `EPERM`.

# FILES

/dev/fd/#
/dev/stdin
/dev/stdout
/dev/stderr

# SEE ALSO

tty(4)

May 31, 2007 | Debian