PIPE(2) System Calls PIPE(2)


pipe - create an interprocess channel


#include <unistd.h>

int pipe(int fildes[2]);

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


The pipe() and pipe2() functions create 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 pipe() call will clear the O_NDELAY,
O_NONBLOCK, and FD_CLOEXEC flags on both file descriptors. The fcntl(2)
function can be used to set these flags.

The pipe2() call will clear the O_NDELAY on both filedescriptors. The
flags argument may be used to specify attributes on both file
descriptors. pipe2() called with a flags value of 0 will behave
identically to pipe(). Values for flags are constructed by a bitwise-
inclusive-OR of flags from the following list, defined in <fcntl.h>.

Both file descriptors will be placed in non-blocking mode.
This corresponds to the O_NONBLOCK flag to fcntl(2).

Both file descriptors will be opened with the FD_CLOEXEC flag
set. Both file descriptors will be closed prior to any future
exec() calls.

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.

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


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


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

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

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

The fildes[2] argument points to an illegal address.

The pipe2() function will also fail if:

The flags argument is illegal. Valid flags are zero or a
bitwise inclusive-OR of O_CLOEXEC and O_NONBLOCK.


See attributes(5) for descriptions of the following attributes:

|Interface Stability | Standard |
|MT-Level | Async-Signal-Safe |


sh(1), fcntl(2), fstat(2), getmsg(2), poll(2), putmsg(2), read(2),
write(2), open(2), attributes(5), standards(5), streamio(7I)


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).

April 19, 2013 PIPE(2)