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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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MKFIFO(3P) POSIX Programmer's Manual MKFIFO(3P)
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.
mkfifo, mkfifoat — make a FIFO special file
#include <sys/stat.h>
int mkfifo(const char *path, mode_t mode);
#include <fcntl.h>
int mkfifoat(int fd, const char *path, mode_t mode);
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
last data access, last data modification, and last file status
change timestamps of the file. Also, the last data modification
and last file status change timestamps of the directory that
contains the new entry shall be marked for update.
The mkfifoat() function shall be equivalent to the mkfifo()
function except in the case where path specifies a relative path.
In this case the newly created FIFO is created relative to the
directory associated with the file descriptor fd instead of the
current working directory. If the access mode of the open file
description associated with the file descriptor is not O_SEARCH,
the function shall check whether directory searches are permitted
using the current permissions of the directory underlying the file
descriptor. If the access mode is O_SEARCH, the function shall not
perform the check.
If mkfifoat() is passed the special value AT_FDCWD in the fd
parameter, the current working directory shall be used and the
behavior shall be identical to a call to mkfifo().
Upon successful completion, these functions shall return 0.
Otherwise, these functions shall return -1 and set errno to
indicate the error. If -1 is returned, no FIFO shall be created.
These functions 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 a component of a pathname is longer than
{NAME_MAX}.
ENOENT A component of the path prefix of path does not name an
existing file or path is an empty string.
ENOENT or ENOTDIR
The path argument contains at least one non-<slash>
character and ends with one or more trailing <slash>
characters. If path without the trailing <slash> characters
would name an existing file, an [ENOENT] error shall not
occur.
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 names an existing file that
is neither a directory nor a symbolic link to a directory.
EROFS The named file resides on a read-only file system.
The mkfifoat() function shall fail if:
EACCES The access mode of the open file description associated
with fd is not O_SEARCH and the permissions of the
directory underlying fd do not permit directory searches.
EBADF The path argument does not specify an absolute path and the
fd argument is neither AT_FDCWD nor a valid file descriptor
open for reading or searching.
ENOTDIR
The path argument is not an absolute path and fd is a file
descriptor associated with a non-directory file.
These functions may fail if:
ELOOP More than {SYMLOOP_MAX} symbolic links were encountered
during resolution of the path argument.
ENAMETOOLONG
The length of a pathname exceeds {PATH_MAX}, or pathname
resolution of a symbolic link produced an intermediate
result with a length that exceeds {PATH_MAX}.
The following sections are informative.
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);
None.
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.
The purpose of the mkfifoat() function is to create a FIFO special
file in directories other than the current working directory
without exposure to race conditions. Any part of the path of a
file could be changed in parallel to a call to mkfifo(), resulting
in unspecified behavior. By opening a file descriptor for the
target directory and using the mkfifoat() function it can be
guaranteed that the newly created FIFO is located relative to the
desired directory.
None.
chmod(3p), mknod(3p), umask(3p)
The Base Definitions volume of POSIX.1‐2017, fcntl.h(0p),
sys_stat.h(0p), sys_types.h(0p)
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 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 .
Any typographical or formatting errors that appear in this page
are most likely to have been introduced during the conversion of
the source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2017 MKFIFO(3P)
Pages that refer to this page: sys_stat.h(0p), mkfifo(1p), pax(1p), chmod(3p), mknod(3p), umask(3p)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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