.\" This manpage is Copyright (C) 1995 James R. Van Zandt .\" and Copyright (C) 2006, 2014 Michael Kerrisk .\" .\" %%%LICENSE_START(VERBATIM) .\" Permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" Permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" Since the Linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. The author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. The author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" Formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%LICENSE_END .\" .\" changed section from 2 to 3, aeb, 950919 .\" .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 .B #include .PP .BI "int mkfifo(const char *" pathname ", mode_t " mode ); .PP .BR "#include " "/* Definition of AT_* constants */" .B #include .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)