man3/mkfifo.3

   1 .\" This manpage is Copyright (C) 1995 James R. Van Zandt <jrv@vanzandt.mv.com>
   2 .\" and Copyright (C) 2006, 2014 Michael Kerrisk
   3 .\"
   4 .\" SPDX-License-Identifier: Linux-man-pages-copyleft
   5 .\"
   6 .\" changed section from 2 to 3, aeb, 950919
   7 .\"
   8 .TH MKFIFO 3 2021-08-27 "Linux man-pages (unreleased)" "Linux Programmer's Manual"
   9 .SH NAME
  10 mkfifo, mkfifoat \- make a FIFO special file (a named pipe)
  11 .SH LIBRARY
  12 Standard C library
  13 .RI ( libc ", " \-lc )
  14 .SH SYNOPSIS
  15 .nf
  16 .B #include <sys/types.h>
  17 .B #include <sys/stat.h>
  18 .PP
  19 .BI "int mkfifo(const char *" pathname ", mode_t " mode );
  20 .PP
  21 .BR "#include <fcntl.h>           " "/* Definition of AT_* constants */"
  22 .B #include <sys/stat.h>
  23 .PP
  24 .BI "int mkfifoat(int " dirfd ", const char *" pathname ", mode_t " mode );
  25 .fi
  26 .PP
  27 .RS -4
  28 Feature Test Macro Requirements for glibc (see
  29 .BR feature_test_macros (7)):
  30 .RE
  31 .PP
  32 .BR mkfifoat ():
  33 .nf
  34     Since glibc 2.10:
  35         _POSIX_C_SOURCE >= 200809L
  36     Before glibc 2.10:
  37         _ATFILE_SOURCE
  38 .fi
  39 .SH DESCRIPTION
  40 .BR mkfifo ()
  41 makes a FIFO special file with name \fIpathname\fP.
  42 \fImode\fP specifies the FIFO's permissions.
  43 It is modified by the
  44 process's \fBumask\fP in the usual way: the permissions of the created
  45 file are \fB(\fP\fImode\fP\fB & \(tiumask)\fP.
  46 .PP
  47 A FIFO special file is similar to a pipe, except that it is created
  48 in a different way.
  49 Instead of being an anonymous communications
  50 channel, a FIFO special file is entered into the filesystem by
  51 calling
  52 .BR mkfifo ().
  53 .PP
  54 Once you have created a FIFO special file in this way, any process can
  55 open it for reading or writing, in the same way as an ordinary file.
  56 However, it has to be open at both ends simultaneously before you can
  57 proceed to do any input or output operations on it.
  58 Opening a FIFO for reading normally blocks until some
  59 other process opens the same FIFO for writing, and vice versa.
  60 See
  61 .BR fifo (7)
  62 for nonblocking handling of FIFO special files.
  63 .SS mkfifoat()
  64 The
  65 .BR mkfifoat ()
  66 function operates in exactly the same way as
  67 .BR mkfifo (),
  68 except for the differences described here.
  69 .PP
  70 If the pathname given in
  71 .I pathname
  72 is relative, then it is interpreted relative to the directory
  73 referred to by the file descriptor
  74 .I dirfd
  75 (rather than relative to the current working directory of
  76 the calling process, as is done by
  77 .BR mkfifo ()
  78 for a relative pathname).
  79 .PP
  80 If
  81 .I pathname
  82 is relative and
  83 .I dirfd
  84 is the special value
  85 .BR AT_FDCWD ,
  86 then
  87 .I pathname
  88 is interpreted relative to the current working
  89 directory of the calling process (like
  90 .BR mkfifo ()).
  91 .PP
  92 If
  93 .I pathname
  94 is absolute, then
  95 .I dirfd
  96 is ignored.
  97 .PP
  98 See
  99 .BR openat (2)
 100 for an explanation of the need for
 101 .BR mkfifoat ().
 102 .SH RETURN VALUE
 103 On success
 104 .BR mkfifo ()
 105 and
 106 .BR mkfifoat ()
 107 return 0.
 108 On error, \-1 is returned and
 109 .I errno
 110 is set to indicate the error.
 111 .SH ERRORS
 112 .TP
 113 .B EACCES
 114 One of the directories in \fIpathname\fP did not allow search
 115 (execute) permission.
 116 .TP
 117 .B EBADF
 118 .RB ( mkfifoat ())
 119 .I pathname
 120 is relative but
 121 .I dirfd
 122 is neither
 123 .B AT_FDCWD
 124 nor a valid file descriptor.
 125 .TP
 126 .B EDQUOT
 127 The user's quota of disk blocks or inodes on the filesystem has been
 128 exhausted.
 129 .TP
 130 .B EEXIST
 131 \fIpathname\fP already exists.
 132 This includes the case where
 133 .I pathname
 134 is a symbolic link, dangling or not.
 135 .TP
 136 .B ENAMETOOLONG
 137 Either the total length of \fIpathname\fP is greater than
 138 \fBPATH_MAX\fP, or an individual filename component has a length
 139 greater than \fBNAME_MAX\fP.
 140 In the GNU system, there is no imposed
 141 limit on overall filename length, but some filesystems may place
 142 limits on the length of a component.
 143 .TP
 144 .B ENOENT
 145 A directory component in \fIpathname\fP does not exist or is a
 146 dangling symbolic link.
 147 .TP
 148 .B ENOSPC
 149 The directory or filesystem has no room for the new file.
 150 .TP
 151 .B ENOTDIR
 152 A component used as a directory in \fIpathname\fP is not, in fact, a
 153 directory.
 154 .TP
 155 .B ENOTDIR
 156 .RB ( mkfifoat ())
 157 .I pathname
 158 is a relative pathname and
 159 .I dirfd
 160 is a file descriptor referring to a file other than a directory.
 161 .TP
 162 .B EROFS
 163 \fIpathname\fP refers to a read-only filesystem.
 164 .SH VERSIONS
 165 .BR mkfifoat ()
 166 was added to glibc in version 2.4.
 167 It is implemented using
 168 .BR mknodat (2),
 169 available on Linux since kernel 2.6.16.
 170 .SH ATTRIBUTES
 171 For an explanation of the terms used in this section, see
 172 .BR attributes (7).
 173 .ad l
 174 .nh
 175 .TS
 176 allbox;
 177 lbx lb lb
 178 l l l.
 179 Interface       Attribute       Value
 180 T{
 181 .BR mkfifo (),
 182 .BR mkfifoat ()
 183 T}      Thread safety   MT-Safe
 184 .TE
 185 .hy
 186 .ad
 187 .sp 1
 188 .SH STANDARDS
 189 .BR mkfifo ():
 190 POSIX.1-2001, POSIX.1-2008.
 191 .PP
 192 .BR mkfifoat ():
 193 POSIX.1-2008.
 194 .SH SEE ALSO
 195 .BR mkfifo (1),
 196 .BR close (2),
 197 .BR open (2),
 198 .BR read (2),
 199 .BR stat (2),
 200 .BR umask (2),
 201 .BR write (2),
 202 .BR fifo (7)