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man pages section 2: System Calls

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Updated: Thursday, June 13, 2019
 
 

pipe(2)

Name

pipe, pipe2 - create an interprocess channel

Synopsis

#include <unistd.h>

int pipe(int fildes[2]);

int pipe2(int fildes[2], int flags);

Description

The pipe() function creates an I/O mechanism called a pipe and returns two file descriptors, fildes[0] and fildes[1]. The files associated with fildes[0] and fildes[1] are streams and are both opened for reading and writing. The O_NDELAY, O_NONBLOCK, and FD_CLOEXEC flags are cleared on both file descriptors. The fcntl(2) function can be used to set these flags.

A read from fildes[0] accesses the data written to fildes[1] on a first-in-first-out (FIFO) basis and a read from fildes[1] accesses the data written to fildes [0] also on a FIFO basis.

The pipe2() function behaves like pipe() but has a second argument which can contain the following open(2) flags: O_CLOEXEC, O_CLOFORK, O_NOSIGPIPE, O_NDELAY and O_NONBLOCK.

Upon successful completion pipe() and pipe2() mark for update the st_atime, st_ctime, and st_mtime fields of the pipe.

Return Values

Upon successful completion, 0 is returned. Otherwise, −1 is returned and errno is set to indicate the error.

Errors

The pipe() and pipe2() functions will fail if:

EMFILE

More than {OPEN_MAX} file descriptors are already in use by this process.

ENFILE

The number of simultaneously open files in the system would exceed a system-imposed limit.

The pipe2() function will fail if:

EINVAL

An invalid flags argument has been passed

Attributes

See attributes(7) for descriptions of the following attributes:

ATTRIBUTE TYPE
ATTRIBUTE VALUE
Interface Stability
Committed
MT-Level
Async-Signal-Safe
Standard

See Also

sh(1), fcntl(2), fstat(2), getmsg(2), poll(2), poll(2), putmsg(2), read(2), write(2), streamio(4I), attributes(7), standards(7)

Notes

Since a pipe is bi-directional, there are two separate flows of data. Therefore, the size (st_size) returned by a call to fstat(2) with argument fildes[ 0] or fildes[1] is the number of bytes available for reading from fildes[0] or fildes[1] respectively. Previously, the size (st_size) returned by a call to fstat() with argument fildes[1] (the write-end) was the number of bytes available for reading from fildes[0] (the read-end).