man-pages/man3/mkfifo.3

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.TH MKFIFO 3 2021-08-27 "GNU" "Linux Programmer's Manual"
.SH NAME
mkfifo, mkfifoat \- make a FIFO special file (a named pipe)
.SH SYNOPSIS
.nf
.B #include <sys/types.h>
.B #include <sys/stat.h>
.PP
.BI "int mkfifo(const char *" pathname ", mode_t " mode );
.PP
.BR "#include <fcntl.h>           " "/* Definition of AT_* constants */"
.B #include <sys/stat.h>
.PP
.BI "int mkfifoat(int " dirfd ", const char *" pathname ", mode_t " mode );
.fi
.PP
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.PP
.BR mkfifoat ():
.nf
    Since glibc 2.10:
        _POSIX_C_SOURCE >= 200809L
    Before glibc 2.10:
        _ATFILE_SOURCE
.fi
.SH DESCRIPTION
.BR mkfifo ()
makes a FIFO special file with name \fIpathname\fP.
\fImode\fP specifies the FIFO's permissions.
It is modified by the
process's \fBumask\fP in the usual way: the permissions of the created
file are \fB(\fP\fImode\fP\fB & \(tiumask)\fP.
.PP
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
.BR mkfifo ().
.PP
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
.BR fifo (7)
for nonblocking handling of FIFO special files.
.SS mkfifoat()
The
.BR mkfifoat ()
function operates in exactly the same way as
.BR mkfifo (),
except for the differences described here.
.PP
If the pathname given in
.I pathname
is relative, then it is interpreted relative to the directory
referred to by the file descriptor
.I dirfd
(rather than relative to the current working directory of
the calling process, as is done by
.BR mkfifo ()
for a relative pathname).
.PP
If
.I pathname
is relative and
.I dirfd
is the special value
.BR AT_FDCWD ,
then
.I pathname
is interpreted relative to the current working
directory of the calling process (like
.BR mkfifo ()).
.PP
If
.I pathname
is absolute, then
.I dirfd
is ignored.
.PP
See
.BR openat (2)
for an explanation of the need for
.BR mkfifoat ().
.SH RETURN VALUE
On success
.BR mkfifo ()
and
.BR mkfifoat ()
return 0.
On error, \-1 is returned and
.I errno
is set to indicate the error.
.SH ERRORS
.TP
.B EACCES
One of the directories in \fIpathname\fP did not allow search
(execute) permission.
.TP
.B EBADF
.RB ( mkfifoat ())
.I pathname
is relative but
.I dirfd
is neither
.B AT_FDCWD
nor a valid file descriptor.
.TP
.B EDQUOT
The user's quota of disk blocks or inodes on the filesystem has been
exhausted.
.TP
.B EEXIST
\fIpathname\fP already exists.
This includes the case where
.I pathname
is a symbolic link, dangling or not.
.TP
.B ENAMETOOLONG
Either the total length of \fIpathname\fP is greater than
\fBPATH_MAX\fP, or an individual filename component has a length
greater than \fBNAME_MAX\fP.
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.
.TP
.B ENOENT
A directory component in \fIpathname\fP does not exist or is a
dangling symbolic link.
.TP
.B ENOSPC
The directory or filesystem has no room for the new file.
.TP
.B ENOTDIR
A component used as a directory in \fIpathname\fP is not, in fact, a
directory.
.TP
.B ENOTDIR
.RB ( mkfifoat ())
.I pathname
is a relative pathname and
.I dirfd
is a file descriptor referring to a file other than a directory.
.TP
.B EROFS
\fIpathname\fP refers to a read-only filesystem.
.SH VERSIONS
.BR mkfifoat ()
was added to glibc in version 2.4.
It is implemented using
.BR mknodat (2),
available on Linux since kernel 2.6.16.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.ad l
.nh
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.BR mkfifo (),
.BR mkfifoat ()
T}	Thread safety	MT-Safe
.TE
.hy
.ad
.sp 1
.SH CONFORMING TO
.BR mkfifo ():
POSIX.1-2001, POSIX.1-2008.
.PP
.BR mkfifoat ():
POSIX.1-2008.
.SH SEE ALSO
.BR mkfifo (1),
.BR close (2),
.BR open (2),
.BR read (2),
.BR stat (2),
.BR umask (2),
.BR write (2),
.BR fifo (7)