# mkfifo

## PROLOG



           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.
    


## NAME



           mkfifo, mkfifoat — make a FIFO special file
    


## SYNOPSIS



           #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_);
    


## 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 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_().
    


## 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_ 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._
    


## 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 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);
    


## 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 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.
    


## FUTURE DIRECTIONS



           None.
    


* * *