1MKFIFO(3P) POSIX Programmer's Manual MKFIFO(3P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
12 mkfifo, mkfifoat — make a FIFO special file
13
15 #include <sys/stat.h>
16 int mkfifo(const char *path, mode_t mode);
18 #include <fcntl.h>
20 int mkfifoat(int fd, const char *path, mode_t mode);
22
24 The mkfifo() function shall create a new FIFO special file named by the
25 pathname pointed to by path. The file permission bits of the new FIFO
26 shall be initialized from mode. The file permission bits of the mode
27 argument shall be modified by the process' file creation mask.
28 When bits in mode other than the file permission bits are set, the
30 effect is implementation-defined.
31 If path names a symbolic link, mkfifo() shall fail and set errno to
33 [EEXIST].
34 The FIFO's user ID shall be set to the process' effective user ID. The
36 FIFO's group ID shall be set to the group ID of the parent directory or
37 to the effective group ID of the process. Implementations shall provide
38 a way to initialize the FIFO's group ID to the group ID of the parent
39 directory. Implementations may, but need not, provide an implementa‐
40 tion-defined way to initialize the FIFO's group ID to the effective
41 group ID of the calling process.
42 Upon successful completion, mkfifo() shall mark for update the last
44 data access, last data modification, and last file status change time‐
45 stamps of the file. Also, the last data modification and last file sta‐
46 tus change timestamps of the directory that contains the new entry
47 shall be marked for update.
48 The mkfifoat() function shall be equivalent to the mkfifo() function
50 except in the case where path specifies a relative path. In this case
51 the newly created FIFO is created relative to the directory associated
52 with the file descriptor fd instead of the current working directory.
53 If the access mode of the open file description associated with the
54 file descriptor is not O_SEARCH, the function shall check whether
55 directory searches are permitted using the current permissions of the
56 directory underlying the file descriptor. If the access mode is
57 O_SEARCH, the function shall not perform the check.
58 If mkfifoat() is passed the special value AT_FDCWD in the fd parameter,
60 the current working directory shall be used and the behavior shall be
61 identical to a call to mkfifo().
62
64 Upon successful completion, these functions shall return 0. Otherwise,
65 these functions shall return -1 and set errno to indicate the error. If
66 -1 is returned, no FIFO shall be created.
67
69 These functions shall fail if:
70 EACCES A component of the path prefix denies search permission, or
72 write permission is denied on the parent directory of the FIFO
73 to be created.
74 EEXIST The named file already exists.
76 ELOOP A loop exists in symbolic links encountered during resolution of
78 the path argument.
79 ENAMETOOLONG
81 The length of a component of a pathname is longer than
82 {NAME_MAX}.
83 ENOENT A component of the path prefix of path does not name an existing
85 file or path is an empty string.
86 ENOENT or ENOTDIR
88 The path argument contains at least one non-<slash> character
89 and ends with one or more trailing <slash> characters. If path
90 without the trailing <slash> characters would name an existing
91 file, an [ENOENT] error shall not occur.
92 ENOSPC The directory that would contain the new file cannot be extended
94 or the file system is out of file-allocation resources.
95 ENOTDIR
97 A component of the path prefix names an existing file that is
98 neither a directory nor a symbolic link to a directory.
99 EROFS The named file resides on a read-only file system.
101 The mkfifoat() function shall fail if:
103 EACCES The access mode of the open file description associated with fd
105 is not O_SEARCH and the permissions of the directory underlying
106 fd do not permit directory searches.
107 EBADF The path argument does not specify an absolute path and the fd
109 argument is neither AT_FDCWD nor a valid file descriptor open
110 for reading or searching.
111 ENOTDIR
113 The path argument is not an absolute path and fd is a file
114 descriptor associated with a non-directory file.
115 These functions may fail if:
117 ELOOP More than {SYMLOOP_MAX} symbolic links were encountered during
119 resolution of the path argument.
120 ENAMETOOLONG
122 The length of a pathname exceeds {PATH_MAX}, or pathname resolu‐
123 tion of a symbolic link produced an intermediate result with a
124 length that exceeds {PATH_MAX}.
125 The following sections are informative.
127
129 Creating a FIFO File
130 The following example shows how to create a FIFO file named
131 /home/cnd/mod_done, with read/write permissions for owner, and with
132 read permissions for group and others.
133 #include <sys/types.h>
136 #include <sys/stat.h>
137 int status;
139 ...
140 status = mkfifo("/home/cnd/mod_done", S_IWUSR | S_IRUSR |
141 S_IRGRP | S_IROTH);
142
144 None.
145
147 The syntax of this function is intended to maintain compatibility with
148 historical implementations of mknod(). The latter function was
149 included in the 1984 /usr/group standard but only for use in creating
150 FIFO special files. The mknod() function was originally excluded from
151 the POSIX.1‐1988 standard as implementation-defined and replaced by
152 mkdir() and mkfifo(). The mknod() function is now included for align‐
153 ment with the Single UNIX Specification.
154 The POSIX.1‐1990 standard required that the group ID of a newly created
156 FIFO be set to the group ID of its parent directory or to the effective
157 group ID of the creating process. FIPS 151‐2 required that implementa‐
158 tions provide a way to have the group ID be set to the group ID of the
159 containing directory, but did not prohibit implementations also sup‐
160 porting a way to set the group ID to the effective group ID of the cre‐
161 ating process. Conforming applications should not assume which group
162 ID will be used. If it matters, an application can use chown() to set
163 the group ID after the FIFO is created, or determine under what condi‐
164 tions the implementation will set the desired group ID.
165 The purpose of the mkfifoat() function is to create a FIFO special file
167 in directories other than the current working directory without expo‐
168 sure to race conditions. Any part of the path of a file could be
169 changed in parallel to a call to mkfifo(), resulting in unspecified
170 behavior. By opening a file descriptor for the target directory and
171 using the mkfifoat() function it can be guaranteed that the newly cre‐
172 ated FIFO is located relative to the desired directory.
173
175 None.
176
178 chmod(), mknod(), umask()
179 The Base Definitions volume of POSIX.1‐2017, <fcntl.h>, <sys_stat.h>,
181 <sys_types.h>
182
184 Portions of this text are reprinted and reproduced in electronic form
185 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
186 table Operating System Interface (POSIX), The Open Group Base Specifi‐
187 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
188 Electrical and Electronics Engineers, Inc and The Open Group. In the
189 event of any discrepancy between this version and the original IEEE and
190 The Open Group Standard, the original IEEE and The Open Group Standard
191 is the referee document. The original Standard can be obtained online
192 at http://www.opengroup.org/unix/online.html .
193 Any typographical or formatting errors that appear in this page are
195 most likely to have been introduced during the conversion of the source
196 files to man page format. To report such errors, see https://www.ker‐
197 nel.org/doc/man-pages/reporting_bugs.html .
198IEEE/The Open Group 2017 MKFIFO(3P)