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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 relative to directory
file descriptor
#include <sys/stat.h>
int mkfifo(const char *path, mode_t mode);
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 file descriptor was opened without O_SEARCH, the
function shall check whether directory searches are permitted using
the current permissions of the directory underlying the file
descriptor. If the file descriptor was opened with 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
names 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 fd was not opened with 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.1‐2008, sys_stat.h(0p),
sys_types.h(0p)
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The Open
Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open
Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
applied.) 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.unix.org/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 2013 MKFIFO(3P)
Pages that refer to this page: sys_stat.h(0p), mkfifo(1p), pax(1p), chmod(3p), mknod(3p), umask(3p)