mkfifo (3p) - Linux Manuals

mkfifo: make a FIFO special file

PROLOG

This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

NAME

mkfifo - make a FIFO special file

SYNOPSIS

#include <sys/stat.h>

int mkfifo(const char *path, mode_t mode);

DESCRIPTION

The mkfifo() function shall create a new FIFO special file named by the pathname pointed to by path. The file permission bits of the new FIFO shall be initialized from mode. The file permission bits of the mode argument shall be modified by the process' file creation mask.

When bits in mode other than the file permission bits are set, the effect is implementation-defined.

If path names a symbolic link, mkfifo() shall fail and set errno to [EEXIST].

The FIFO's user ID shall be set to the process' effective user ID. The FIFO's group ID shall be set to the group ID of the parent directory or to the effective group ID of the process. Implementations shall provide a way to initialize the FIFO's group ID to the group ID of the parent directory. Implementations may, but need not, provide an implementation-defined way to initialize the FIFO's group ID to the effective group ID of the calling process.

Upon successful completion, mkfifo() shall mark for update the st_atime, st_ctime, and st_mtime fields of the file. Also, the st_ctime and st_mtime fields of the directory that contains the new entry shall be marked for update.

RETURN VALUE

Upon successful completion, 0 shall be returned. Otherwise, -1 shall be returned, no FIFO shall be created, and errno shall be set to indicate the error.

ERRORS

The mkfifo() function shall fail if:

EACCES

A component of the path prefix denies search permission, or write permission is denied on the parent directory of the FIFO to be created.

EEXIST

The named file already exists.

ELOOP

A loop exists in symbolic links encountered during resolution of the path argument.

ENAMETOOLONG

The length of the path argument exceeds {PATH_MAX} or a pathname component is longer than {NAME_MAX}.

ENOENT

A component of the path prefix specified by path does not name an existing directory or path is an empty string.

ENOSPC

The directory that would contain the new file cannot be extended or the file system is out of file-allocation resources.

ENOTDIR

A component of the path prefix is not a directory.

EROFS

The named file resides on a read-only file system.

The mkfifo() function may fail if:

ELOOP

More than {SYMLOOP_MAX} symbolic links were encountered during resolution of the path argument.

ENAMETOOLONG

As a result of encountering a symbolic link in resolution of the path argument, the length of the substituted pathname string exceeded {PATH_MAX}.

The following sections are informative.

EXAMPLES

Creating a FIFO File

The following example shows how to create a FIFO file named /home/cnd/mod_done, with read/write permissions for owner, and with read permissions for group and others.

#include <sys/types.h>
#include <sys/stat.h>


int status;
...
status = mkfifo("/home/cnd/mod_done", S_IWUSR | S_IRUSR |
    S_IRGRP | S_IROTH);

APPLICATION USAGE

None.

RATIONALE

The syntax of this function is intended to maintain compatibility with historical implementations of mknod(). The latter function was included in the 1984 /usr/group standard but only for use in creating FIFO special files. The mknod() function was originally excluded from the POSIX.1-1988 standard as implementation-defined and replaced by mkdir() and mkfifo(). The mknod() function is now included for alignment with the Single UNIX Specification.

The POSIX.1-1990 standard required that the group ID of a newly created FIFO be set to the group ID of its parent directory or to the effective group ID of the creating process. FIPS 151-2 required that implementations provide a way to have the group ID be set to the group ID of the containing directory, but did not prohibit implementations also supporting a way to set the group ID to the effective group ID of the creating process. Conforming applications should not assume which group ID will be used. If it matters, an application can use chown() to set the group ID after the FIFO is created, or determine under what conditions the implementation will set the desired group ID.

FUTURE DIRECTIONS

None.

COPYRIGHT

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .