1fcntl.h(0P) POSIX Programmer's Manual fcntl.h(0P)
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 fcntl.h — file control options
13
15 #include <fcntl.h>
16
18 The <fcntl.h> header shall define the following symbolic constants for
19 the cmd argument used by fcntl(). The values shall be unique and shall
20 be suitable for use in #if preprocessing directives.
21 F_DUPFD Duplicate file descriptor.
23 F_DUPFD_CLOEXEC
25 Duplicate file descriptor with the close-on-exec flag
26 FD_CLOEXEC set.
27 F_GETFD Get file descriptor flags.
29 F_SETFD Set file descriptor flags.
31 F_GETFL Get file status flags and file access modes.
33 F_SETFL Set file status flags.
35 F_GETLK Get record locking information.
37 F_SETLK Set record locking information.
39 F_SETLKW Set record locking information; wait if blocked.
41 F_GETOWN Get process or process group ID to receive SIGURG signals.
43 F_SETOWN Set process or process group ID to receive SIGURG signals.
45 The <fcntl.h> header shall define the following symbolic constant used
47 for the fcntl() file descriptor flags, which shall be suitable for use
48 in #if preprocessing directives.
49 FD_CLOEXEC Close the file descriptor upon execution of an exec family
51 function.
52 The <fcntl.h> header shall also define the following symbolic constants
54 for the l_type argument used for record locking with fcntl(). The val‐
55 ues shall be unique and shall be suitable for use in #if preprocessing
56 directives.
57 F_RDLCK Shared or read lock.
59 F_UNLCK Unlock.
61 F_WRLCK Exclusive or write lock.
63 The <fcntl.h> header shall define the values used for l_whence,
65 SEEK_SET, SEEK_CUR, and SEEK_END as described in <stdio.h>.
66 The <fcntl.h> header shall define the following symbolic constants as
68 file creation flags for use in the oflag value to open() and openat().
69 The values shall be bitwise-distinct and shall be suitable for use in
70 #if preprocessing directives.
71 O_CLOEXEC The FD_CLOEXEC flag associated with the new descriptor
73 shall be set to close the file descriptor upon execution of
74 an exec family function.
75 O_CREAT Create file if it does not exist.
77 O_DIRECTORY Fail if file is a non-directory file.
79 O_EXCL Exclusive use flag.
81 O_NOCTTY Do not assign controlling terminal.
83 O_NOFOLLOW Do not follow symbolic links.
85 O_TRUNC Truncate flag.
87 O_TTY_INIT Set the termios structure terminal parameters to a state
89 that provides conforming behavior; see Section 11.2, Param‐
90 eters that Can be Set.
91 The O_TTY_INIT flag can have the value zero and in this case it need
93 not be bitwise-distinct from the other flags.
94 The <fcntl.h> header shall define the following symbolic constants for
96 use as file status flags for open(), openat(), and fcntl(). The values
97 shall be suitable for use in #if preprocessing directives.
98 O_APPEND Set append mode.
100 O_DSYNC Write according to synchronized I/O data integrity comple‐
102 tion.
103 O_NONBLOCK Non-blocking mode.
105 O_RSYNC Synchronized read I/O operations.
107 O_SYNC Write according to synchronized I/O file integrity comple‐
109 tion.
110 The <fcntl.h> header shall define the following symbolic constant for
112 use as the mask for file access modes. The value shall be suitable for
113 use in #if preprocessing directives.
114 O_ACCMODE Mask for file access modes.
116 The <fcntl.h> header shall define the following symbolic constants for
118 use as the file access modes for open(), openat(), and fcntl(). The
119 values shall be unique, except that O_EXEC and O_SEARCH may have equal
120 values. The values shall be suitable for use in #if preprocessing
121 directives.
122 O_EXEC Open for execute only (non-directory files). The result is
124 unspecified if this flag is applied to a directory.
125 O_RDONLY Open for reading only.
127 O_RDWR Open for reading and writing.
129 O_SEARCH Open directory for search only. The result is unspecified
131 if this flag is applied to a non-directory file.
132 O_WRONLY Open for writing only.
134 The <fcntl.h> header shall define the symbolic constants for file modes
136 for use as values of mode_t as described in <sys/stat.h>.
137 The <fcntl.h> header shall define the following symbolic constant as a
139 special value used in place of a file descriptor for the *at() func‐
140 tions which take a directory file descriptor as a parameter:
141 AT_FDCWD Use the current working directory to determine the target
143 of relative file paths.
144 The <fcntl.h> header shall define the following symbolic constant as a
146 value for the flag used by faccessat():
147 AT_EACCESS Check access using effective user and group ID.
149 The <fcntl.h> header shall define the following symbolic constant as a
151 value for the flag used by fstatat(), fchmodat(), fchownat(), and uti‐
152 mensat():
153 AT_SYMLINK_NOFOLLOW
155 Do not follow symbolic links.
156 The <fcntl.h> header shall define the following symbolic constant as a
158 value for the flag used by linkat():
159 AT_SYMLINK_FOLLOW
161 Follow symbolic link.
162 The <fcntl.h> header shall define the following symbolic constant as a
164 value for the flag used by unlinkat():
165 AT_REMOVEDIR
167 Remove directory instead of file.
168 The <fcntl.h> header shall define the following symbolic constants for
170 the advice argument used by posix_fadvise():
171 POSIX_FADV_DONTNEED
173 The application expects that it will not access the specified
174 data in the near future.
175 POSIX_FADV_NOREUSE
177 The application expects to access the specified data once and
178 then not reuse it thereafter.
179 POSIX_FADV_NORMAL
181 The application has no advice to give on its behavior with
182 respect to the specified data. It is the default characteristic
183 if no advice is given for an open file.
184 POSIX_FADV_RANDOM
186 The application expects to access the specified data in a random
187 order.
188 POSIX_FADV_SEQUENTIAL
190 The application expects to access the specified data sequentially
191 from lower offsets to higher offsets.
192 POSIX_FADV_WILLNEED
194 The application expects to access the specified data in the near
195 future.
196 The <fcntl.h> header shall define the flock structure describing a file
198 lock. It shall include the following members:
199 short l_type Type of lock; F_RDLCK, F_WRLCK, F_UNLCK.
202 short l_whence Flag for starting offset.
203 off_t l_start Relative offset in bytes.
204 off_t l_len Size; if 0 then until EOF.
205 pid_t l_pid Process ID of the process holding the lock; returned with F_GETLK.
206 The <fcntl.h> header shall define the mode_t, off_t, and pid_t types as
208 described in <sys/types.h>.
209 The following shall be declared as functions and may also be defined as
211 macros. Function prototypes shall be provided.
212 int creat(const char *, mode_t);
215 int fcntl(int, int, ...);
216 int open(const char *, int, ...);
217 int openat(int, const char *, int, ...);
218 int posix_fadvise(int, off_t, off_t, int);
219 int posix_fallocate(int, off_t, off_t);
220 Inclusion of the <fcntl.h> header may also make visible all symbols
222 from <sys/stat.h> and <unistd.h>.
223 The following sections are informative.
225
227 Although no existing implementation defines AT_SYMLINK_FOLLOW and
228 AT_SYMLINK_NOFOLLOW as the same numeric value, POSIX.1‐2008 does not
229 prohibit that as the two constants are not used with the same inter‐
230 faces.
231
233 While many of the symbolic constants introduced in the <fcntl.h> header
234 do not strictly need to be used in #if preprocessor directives, wide‐
235 spread historic practice has defined them as macros that are usable in
236 such constructs, and examination of existing applications has shown
237 that they are occasionally used in such a way. Therefore it was decided
238 to retain this requirement on an implementation in POSIX.1‐2008.
239
241 None.
242
244 <stdio.h>, <sys_stat.h>, <sys_types.h>, <unistd.h>
245 The System Interfaces volume of POSIX.1‐2017, creat(), exec, fcntl(),
247 futimens(), open(), posix_fadvise(), posix_fallocate(), posix_madvise()
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250 Portions of this text are reprinted and reproduced in electronic form
251 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
252 table Operating System Interface (POSIX), The Open Group Base Specifi‐
253 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
254 Electrical and Electronics Engineers, Inc and The Open Group. In the
255 event of any discrepancy between this version and the original IEEE and
256 The Open Group Standard, the original IEEE and The Open Group Standard
257 is the referee document. The original Standard can be obtained online
258 at http://www.opengroup.org/unix/online.html .
259 Any typographical or formatting errors that appear in this page are
261 most likely to have been introduced during the conversion of the source
262 files to man page format. To report such errors, see https://www.ker‐
263 nel.org/doc/man-pages/reporting_bugs.html .
264IEEE/The Open Group 2017 fcntl.h(0P)