1MKNOD(3P) POSIX Programmer's Manual MKNOD(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
13 mknod, mknodat — make directory, special file, or regular file
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16 #include <sys/stat.h>
17 int mknod(const char *path, mode_t mode, dev_t dev);
19 int mknodat(int fd, const char *path, mode_t mode, dev_t dev);
20
22 The mknod() function shall create a new file named by the pathname to
23 which the argument path points.
24 The file type for path is OR'ed into the mode argument, and the appli‐
26 cation shall select one of the following symbolic constants:
27 ┌───────────┬──────────────────────────────────┐
29 │ Name │ Description │
30 ├───────────┼──────────────────────────────────┤
31 │S_IFIFO │ FIFO-special │
32 │S_IFCHR │ Character-special (non-portable) │
33 │S_IFDIR │ Directory (non-portable) │
34 │S_IFBLK │ Block-special (non-portable) │
35 │S_IFREG │ Regular (non-portable) │
36 └───────────┴──────────────────────────────────┘
37 The only portable use of mknod() is to create a FIFO-special file. If
38 mode is not S_IFIFO or dev is not 0, the behavior of mknod() is unspec‐
39 ified.
40 The permissions for the new file are OR'ed into the mode argument, and
42 may be selected from any combination of the following symbolic con‐
43 stants:
44 ┌───────────┬─────────────────────────────────────────────┐
46 │ Name │ Description │
47 ├───────────┼─────────────────────────────────────────────┤
48 │S_ISUID │ Set user ID on execution. │
49 │S_ISGID │ Set group ID on execution. │
50 │S_IRWXU │ Read, write, or execute (search) by owner. │
51 │S_IRUSR │ Read by owner. │
52 │S_IWUSR │ Write by owner. │
53 │S_IXUSR │ Execute (search) by owner. │
54 │S_IRWXG │ Read, write, or execute (search) by group. │
55 │S_IRGRP │ Read by group. │
56 │S_IWGRP │ Write by group. │
57 │S_IXGRP │ Execute (search) by group. │
58 │S_IRWXO │ Read, write, or execute (search) by others. │
59 │S_IROTH │ Read by others. │
60 │S_IWOTH │ Write by others. │
61 │S_IXOTH │ Execute (search) by others. │
62 │S_ISVTX │ On directories, restricted deletion flag. │
63 └───────────┴─────────────────────────────────────────────┘
64 The user ID of the file shall be initialized to the effective user ID
65 of the process. The group ID of the file shall be initialized to either
66 the effective group ID of the process or the group ID of the parent
67 directory. Implementations shall provide a way to initialize the file's
68 group ID to the group ID of the parent directory. Implementations may,
69 but need not, provide an implementation-defined way to initialize the
70 file's group ID to the effective group ID of the calling process. The
71 owner, group, and other permission bits of mode shall be modified by
72 the file mode creation mask of the process. The mknod() function shall
73 clear each bit whose corresponding bit in the file mode creation mask
74 of the process is set.
75 If path names a symbolic link, mknod() shall fail and set errno to
77 [EEXIST].
78 Upon successful completion, mknod() shall mark for update the last data
80 access, last data modification, and last file status change timestamps
81 of the file. Also, the last data modification and last file status
82 change timestamps of the directory that contains the new entry shall be
83 marked for update.
84 Only a process with appropriate privileges may invoke mknod() for file
86 types other than FIFO-special.
87 The mknodat() function shall be equivalent to the mknod() function
89 except in the case where path specifies a relative path. In this case
90 the newly created directory, special file, or regular file is located
91 relative to the directory associated with the file descriptor fd
92 instead of the current working directory. If the file descriptor was
93 opened without O_SEARCH, the function shall check whether directory
94 searches are permitted using the current permissions of the directory
95 underlying the file descriptor. If the file descriptor was opened with
96 O_SEARCH, the function shall not perform the check.
97 If mknodat() is passed the special value AT_FDCWD in the fd parameter,
99 the current working directory shall be used and the behavior shall be
100 identical to a call to mknod().
101
103 Upon successful completion, these functions shall return 0. Otherwise,
104 these functions shall return −1 and set errno to indicate the error. If
105 −1 is returned, the new file shall not be created.
106
108 These functions shall fail if:
109 EACCES A component of the path prefix denies search permission, or
111 write permission is denied on the parent directory.
112 EEXIST The named file exists.
114 EINVAL An invalid argument exists.
116 EIO An I/O error occurred while accessing the file system.
118 ELOOP A loop exists in symbolic links encountered during resolution of
120 the path argument.
121 ENAMETOOLONG
123 The length of a component of a pathname is longer than
124 {NAME_MAX}.
125 ENOENT A component of the path prefix of path does not name an existing
127 file or path is an empty string.
128 ENOENT or ENOTDIR
130 The path argument contains at least one non-<slash> character
131 and ends with one or more trailing <slash> characters. If path
132 names an existing file, an [ENOENT] error shall not occur.
133 ENOSPC The directory that would contain the new file cannot be extended
135 or the file system is out of file allocation resources.
136 ENOTDIR
138 A component of the path prefix names an existing file that is
139 neither a directory nor a symbolic link to a directory.
140 EPERM The invoking process does not have appropriate privileges and
142 the file type is not FIFO-special.
143 EROFS The directory in which the file is to be created is located on a
145 read-only file system.
146 The mknodat() function shall fail if:
148 EACCES fd was not opened with O_SEARCH and the permissions of the
150 directory underlying fd do not permit directory searches.
151 EBADF The path argument does not specify an absolute path and the fd
153 argument is neither AT_FDCWD nor a valid file descriptor open
154 for reading or searching.
155 ENOTDIR
157 The path argument is not an absolute path and fd is a file
158 descriptor associated with a non-directory file.
159 These functions may fail if:
161 ELOOP More than {SYMLOOP_MAX} symbolic links were encountered during
163 resolution of the path argument.
164 ENAMETOOLONG
166 The length of a pathname exceeds {PATH_MAX}, or pathname resolu‐
167 tion of a symbolic link produced an intermediate result with a
168 length that exceeds {PATH_MAX}.
169 The following sections are informative.
171
173 Creating a FIFO Special File
174 The following example shows how to create a FIFO special file named
175 /home/cnd/mod_done, with read/write permissions for owner, and with
176 read permissions for group and others.
177 #include <sys/types.h>
179 #include <sys/stat.h>
180 dev_t dev;
182 int status;
183 ...
184 status = mknod("/home/cnd/mod_done", S_IFIFO | S_IWUSR |
185 S_IRUSR | S_IRGRP | S_IROTH, dev);
186
188 The mkfifo() function is preferred over this function for making FIFO
189 special files.
190
192 The POSIX.1‐1990 standard required that the group ID of a newly created
193 file be set to the group ID of its parent directory or to the effective
194 group ID of the creating process. FIPS 151‐2 required that implementa‐
195 tions provide a way to have the group ID be set to the group ID of the
196 containing directory, but did not prohibit implementations also sup‐
197 porting a way to set the group ID to the effective group ID of the cre‐
198 ating process. Conforming applications should not assume which group
199 ID will be used. If it matters, an application can use chown() to set
200 the group ID after the file is created, or determine under what condi‐
201 tions the implementation will set the desired group ID.
202 The purpose of the mknodat() function is to create directories, special
204 files, or regular files in directories other than the current working
205 directory without exposure to race conditions. Any part of the path of
206 a file could be changed in parallel to a call to mknod(), resulting in
207 unspecified behavior. By opening a file descriptor for the target
208 directory and using the mknodat() function it can be guaranteed that
209 the newly created directory, special file, or regular file is located
210 relative to the desired directory.
211
213 None.
214
216 chmod(), creat(), exec, fstatat(), mkdir(), mkfifo(), open(), umask()
217 The Base Definitions volume of POSIX.1‐2008, <sys_stat.h>
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221 Portions of this text are reprinted and reproduced in electronic form
222 from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
223 -- Portable Operating System Interface (POSIX), The Open Group Base
224 Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
225 cal and Electronics Engineers, Inc and The Open Group. (This is
226 POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
227 event of any discrepancy between this version and the original IEEE and
228 The Open Group Standard, the original IEEE and The Open Group Standard
229 is the referee document. The original Standard can be obtained online
230 at http://www.unix.org/online.html .
231 Any typographical or formatting errors that appear in this page are
233 most likely to have been introduced during the conversion of the source
234 files to man page format. To report such errors, see https://www.ker‐
235 nel.org/doc/man-pages/reporting_bugs.html .
236IEEE/The Open Group 2013 MKNOD(3P)