MKFIFO(3P) POSIX Programmer's Manual MKFIFO(3P)
PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the correspond-
ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.
NAME
mkfifo, mkfifoat -- make a FIFO special file relative to directory file descriptor
SYNOPSIS
#include <sys/stat.h>
int mkfifo(const char *path, mode_t mode);
int mkfifoat(int fd, 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 effec-
tive 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 time-
stamps 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 direc-
tory. If the file descriptor was opened without O_SEARCH, the function shall check whether directory searches are permitted using the cur-
rent 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().
RETURN VALUE
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.
ERRORS
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.
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 per-
missions 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 align-
ment 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 cre-
ated FIFO is located relative to the desired directory.
FUTURE DIRECTIONS
None.
SEE ALSO
chmod(), mknod(), umask()
The Base Definitions volume of POSIX.1-2008, <sys_stat.h>, <sys_types.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technol-
ogy -- 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 Stan-
dard 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)