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MKFIFO(2) System Calls Manual MKFIFO(2)

mkfifo, mkfifoat — make a FIFO file

#include <sys/stat.h>

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

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

int
mkfifoat(int fd, const char *path, mode_t mode);

() creates a new FIFO file with name path. The access permissions are specified by mode and restricted by the umask(2) of the calling process.

The FIFO's owner ID is set to the process's effective user ID. The FIFO's group ID is set to that of the parent directory in which it is created.

The () function is equivalent to mkfifo() except that where path specifies a relative path, the newly created FIFO is created relative to the directory associated with file descriptor fd instead of the current working directory.

If () is passed the special value AT_FDCWD (defined in <fcntl.h>) in the fd parameter, the current working directory is used and the behavior is identical to a call to mkfifo().

Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

mkfifo() and mkfifoat() will fail and no FIFO will be created if:

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The kernel has not been configured to support FIFOs.
[]
A component of the path prefix is not a directory.
[]
A component of a pathname exceeded NAME_MAX characters, or an entire pathname (including the terminating NUL) exceeded PATH_MAX bytes.
[]
A component of the path prefix does not exist.
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Search permission is denied for a component of the path prefix.
[]
Too many symbolic links were encountered in translating the pathname.
[]
The named file resides on a read-only file system.
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The named file exists.
[]
The directory in which the entry for the new FIFO is being placed cannot be extended because there is no space left on the file system containing the directory.
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There are no free inodes on the file system on which the FIFO is being created.
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The directory in which the entry for the new FIFO is being placed cannot be extended because the user's quota of disk blocks on the file system containing the directory has been exhausted.
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The user's quota of inodes on the file system on which the FIFO is being created has been exhausted.
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An I/O error occurred while making the directory entry or allocating the inode.
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An I/O error occurred while reading from or writing to the file system.
[]
path points outside the process's allocated address space.

Additionally, mkfifoat() will fail if:

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The path argument specifies a relative path and the fd argument is neither AT_FDCWD nor a valid file descriptor.
[]
The path argument specifies a relative path and the fd argument is a valid file descriptor but it does not reference a directory.
[]
The path argument specifies a relative path but search permission is denied for the directory which the fd file descriptor references.

chmod(2), stat(2), umask(2)

The mkfifo() and mkfifoat() functions conform to IEEE Std 1003.1-2008 (“POSIX.1”).

The mkfifoat() function appeared in OpenBSD 5.0.

May 31, 2015 OpenBSD-7.6