mkfifo(3) Library Functions Manual mkfifo(3)

mkfifo, mkfifoat - make a FIFO special file (a named pipe)

Standard C library (libc, -lc)

#include <sys/types.h>
#include <sys/stat.h>
int mkfifo(const char *pathname, mode_t mode);
#include <fcntl.h>           /* Definition of AT_* constants */
#include <sys/stat.h>
int mkfifoat(int dirfd, const char *pathname, mode_t mode);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

mkfifoat():

    Since glibc 2.10:
        _POSIX_C_SOURCE >= 200809L
    Before glibc 2.10:
        _ATFILE_SOURCE

mkfifo() makes a FIFO special file with name pathname. mode specifies the FIFO's permissions. It is modified by the process's umask in the usual way: the permissions of the created file are (mode & ~umask).

A FIFO special file is similar to a pipe, except that it is created in a different way. Instead of being an anonymous communications channel, a FIFO special file is entered into the filesystem by calling mkfifo().

Once you have created a FIFO special file in this way, any process can open it for reading or writing, in the same way as an ordinary file. However, it has to be open at both ends simultaneously before you can proceed to do any input or output operations on it. Opening a FIFO for reading normally blocks until some other process opens the same FIFO for writing, and vice versa. See fifo(7) for nonblocking handling of FIFO special files.

The mkfifoat() function operates in exactly the same way as mkfifo(), except for the differences described here.

If the pathname given in pathname is relative, then it is interpreted relative to the directory referred to by the file descriptor dirfd (rather than relative to the current working directory of the calling process, as is done by mkfifo() for a relative pathname).

If pathname is relative and dirfd is the special value AT_FDCWD, then pathname is interpreted relative to the current working directory of the calling process (like mkfifo()).

If pathname is absolute, then dirfd is ignored.

See openat(2) for an explanation of the need for mkfifoat().

On success mkfifo() and mkfifoat() return 0. On error, -1 is returned and errno is set to indicate the error.

One of the directories in pathname did not allow search (execute) permission.
(mkfifoat()) pathname is relative but dirfd is neither AT_FDCWD nor a valid file descriptor.
The user's quota of disk blocks or inodes on the filesystem has been exhausted.
pathname already exists. This includes the case where pathname is a symbolic link, dangling or not.
Either the total length of pathname is greater than PATH_MAX, or an individual filename component has a length greater than NAME_MAX. In the GNU system, there is no imposed limit on overall filename length, but some filesystems may place limits on the length of a component.
A directory component in pathname does not exist or is a dangling symbolic link.
The directory or filesystem has no room for the new file.
A component used as a directory in pathname is not, in fact, a directory.
(mkfifoat()) pathname is a relative pathname and dirfd is a file descriptor referring to a file other than a directory.
pathname refers to a read-only filesystem.

For an explanation of the terms used in this section, see attributes(7).

Interface Attribute Value
mkfifo (), mkfifoat () Thread safety MT-Safe

It is implemented using mknodat(2).

POSIX.1-2008.

POSIX.1-2001.
glibc 2.4. POSIX.1-2008.

mkfifo(1), close(2), open(2), read(2), stat(2), umask(2), write(2), fifo(7)

2023-10-31 Linux man-pages 6.7