1unistd.h(0P) POSIX Programmer's Manual unistd.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 unistd.h — standard symbolic constants and types
13
15 #include <unistd.h>
16
18 The <unistd.h> header defines miscellaneous symbolic constants and
19 types, and declares miscellaneous functions. The actual values of the
20 constants are unspecified except as shown. The contents of this header
21 are shown below.
22 Version Test Macros
24 The <unistd.h> header shall define the following symbolic constants.
25 The values shall be suitable for use in #if preprocessing directives.
26 _POSIX_VERSION
28 Integer value indicating version of this standard (C-language
29 binding) to which the implementation conforms. For implementa‐
30 tions conforming to POSIX.1‐2008, the value shall be 200809L.
31 _POSIX2_VERSION
33 Integer value indicating version of the Shell and Utilities vol‐
34 ume of POSIX.1 to which the implementation conforms. For imple‐
35 mentations conforming to POSIX.1‐2008, the value shall be
36 200809L. For profile implementations that define _POSIX_SUBPRO‐
37 FILE (see Section 2.1.5.1, Subprofiling Considerations) in
38 <unistd.h>, _POSIX2_VERSION may be left undefined or be defined
39 with the value -1 to indicate that the Shell and Utilities volume
40 of POSIX.1 is not supported. In this case, a call to
41 sysconf(_SC_2_VERSION) shall return either 200809L or -1 indicat‐
42 ing that the Shell and Utilities volume of POSIX.1 is or is not,
43 respectively, supported at runtime.
44 The <unistd.h> header shall define the following symbolic constant only
46 if the implementation supports the XSI option; see Section 2.1.4, XSI
47 Conformance. If defined, its value shall be suitable for use in #if
48 preprocessing directives.
49 _XOPEN_VERSION
51 Integer value indicating version of the X/Open Portability Guide
52 to which the implementation conforms. The value shall be 700.
53 Constants for Options and Option Groups
55 The following symbolic constants, if defined in <unistd.h>, shall have
56 a value of -1, 0, or greater, unless otherwise specified below. For
57 profile implementations that define _POSIX_SUBPROFILE (see Section
58 2.1.5.1, Subprofiling Considerations) in <unistd.h>, constants
59 described below as always having a value greater than zero need not be
60 defined and, if defined, may have a value of -1, 0, or greater. The
61 values shall be suitable for use in #if preprocessing directives.
62 If a symbolic constant is not defined or is defined with the value -1,
64 the option is not supported for compilation. If it is defined with a
65 value greater than zero, the option shall always be supported when the
66 application is executed. If it is defined with the value zero, the
67 option shall be supported for compilation and might or might not be
68 supported at runtime. See Section 2.1.6, Options for further informa‐
69 tion about the conformance requirements of these three categories of
70 support.
71 _POSIX_ADVISORY_INFO
73 The implementation supports the Advisory Information option. If
74 this symbol is defined in <unistd.h>, it shall be defined to be
75 -1, 0, or 200809L. The value of this symbol reported by sysconf()
76 shall either be -1 or 200809L.
77 _POSIX_ASYNCHRONOUS_IO
79 The implementation supports asynchronous input and output. This
80 symbol shall always be set to the value 200809L.
81 _POSIX_BARRIERS
83 The implementation supports barriers. This symbol shall always
84 be set to the value 200809L.
85 _POSIX_CHOWN_RESTRICTED
87 The use of chown() and fchown() is restricted to a process with
88 appropriate privileges, and to changing the group ID of a file
89 only to the effective group ID of the process or to one of its
90 supplementary group IDs. This symbol shall be defined with a
91 value other than -1.
92 _POSIX_CLOCK_SELECTION
94 The implementation supports clock selection. This symbol shall
95 always be set to the value 200809L.
96 _POSIX_CPUTIME
98 The implementation supports the Process CPU-Time Clocks option.
99 If this symbol is defined in <unistd.h>, it shall be defined to
100 be -1, 0, or 200809L. The value of this symbol reported by
101 sysconf() shall either be -1 or 200809L.
102 _POSIX_FSYNC
104 The implementation supports the File Synchronization option. If
105 this symbol is defined in <unistd.h>, it shall be defined to be
106 -1, 0, or 200809L. The value of this symbol reported by sysconf()
107 shall either be -1 or 200809L.
108 _POSIX_IPV6
110 The implementation supports the IPv6 option. If this symbol is
111 defined in <unistd.h>, it shall be defined to be -1, 0, or
112 200809L. The value of this symbol reported by sysconf() shall
113 either be -1 or 200809L.
114 _POSIX_JOB_CONTROL
116 The implementation supports job control. This symbol shall always
117 be set to a value greater than zero.
118 _POSIX_MAPPED_FILES
120 The implementation supports memory mapped Files. This symbol
121 shall always be set to the value 200809L.
122 _POSIX_MEMLOCK
124 The implementation supports the Process Memory Locking option.
125 If this symbol is defined in <unistd.h>, it shall be defined to
126 be -1, 0, or 200809L. The value of this symbol reported by
127 sysconf() shall either be -1 or 200809L.
128 _POSIX_MEMLOCK_RANGE
130 The implementation supports the Range Memory Locking option. If
131 this symbol is defined in <unistd.h>, it shall be defined to be
132 -1, 0, or 200809L. The value of this symbol reported by sysconf()
133 shall either be -1 or 200809L.
134 _POSIX_MEMORY_PROTECTION
136 The implementation supports memory protection. This symbol shall
137 always be set to the value 200809L.
138 _POSIX_MESSAGE_PASSING
140 The implementation supports the Message Passing option. If this
141 symbol is defined in <unistd.h>, it shall be defined to be -1, 0,
142 or 200809L. The value of this symbol reported by sysconf() shall
143 either be -1 or 200809L.
144 _POSIX_MONOTONIC_CLOCK
146 The implementation supports the Monotonic Clock option. If this
147 symbol is defined in <unistd.h>, it shall be defined to be -1, 0,
148 or 200809L. The value of this symbol reported by sysconf() shall
149 either be -1 or 200809L.
150 _POSIX_NO_TRUNC
152 Pathname components longer than {NAME_MAX} generate an error.
153 This symbol shall be defined with a value other than -1.
154 _POSIX_PRIORITIZED_IO
156 The implementation supports the Prioritized Input and Output
157 option. If this symbol is defined in <unistd.h>, it shall be
158 defined to be -1, 0, or 200809L. The value of this symbol
159 reported by sysconf() shall either be -1 or 200809L.
160 _POSIX_PRIORITY_SCHEDULING
162 The implementation supports the Process Scheduling option. If
163 this symbol is defined in <unistd.h>, it shall be defined to be
164 -1, 0, or 200809L. The value of this symbol reported by sysconf()
165 shall either be -1 or 200809L.
166 _POSIX_RAW_SOCKETS
168 The implementation supports the Raw Sockets option. If this sym‐
169 bol is defined in <unistd.h>, it shall be defined to be -1, 0, or
170 200809L. The value of this symbol reported by sysconf() shall
171 either be -1 or 200809L.
172 _POSIX_READER_WRITER_LOCKS
174 The implementation supports read-write locks. This symbol shall
175 always be set to the value 200809L.
176 _POSIX_REALTIME_SIGNALS
178 The implementation supports realtime signals. This symbol shall
179 always be set to the value 200809L.
180 _POSIX_REGEXP
182 The implementation supports the Regular Expression Handling
183 option. This symbol shall always be set to a value greater than
184 zero.
185 _POSIX_SAVED_IDS
187 Each process has a saved set-user-ID and a saved set-group-ID.
188 This symbol shall always be set to a value greater than zero.
189 _POSIX_SEMAPHORES
191 The implementation supports semaphores. This symbol shall always
192 be set to the value 200809L.
193 _POSIX_SHARED_MEMORY_OBJECTS
195 The implementation supports the Shared Memory Objects option. If
196 this symbol is defined in <unistd.h>, it shall be defined to be
197 -1, 0, or 200809L. The value of this symbol reported by sysconf()
198 shall either be -1 or 200809L.
199 _POSIX_SHELL
201 The implementation supports the POSIX shell. This symbol shall
202 always be set to a value greater than zero.
203 _POSIX_SPAWN
205 The implementation supports the Spawn option. If this symbol is
206 defined in <unistd.h>, it shall be defined to be -1, 0, or
207 200809L. The value of this symbol reported by sysconf() shall
208 either be -1 or 200809L.
209 _POSIX_SPIN_LOCKS
211 The implementation supports spin locks. This symbol shall always
212 be set to the value 200809L.
213 _POSIX_SPORADIC_SERVER
215 The implementation supports the Process Sporadic Server option.
216 If this symbol is defined in <unistd.h>, it shall be defined to
217 be -1, 0, or 200809L. The value of this symbol reported by
218 sysconf() shall either be -1 or 200809L.
219 _POSIX_SYNCHRONIZED_IO
221 The implementation supports the Synchronized Input and Output
222 option. If this symbol is defined in <unistd.h>, it shall be
223 defined to be -1, 0, or 200809L. The value of this symbol
224 reported by sysconf() shall either be -1 or 200809L.
225 _POSIX_THREAD_ATTR_STACKADDR
227 The implementation supports the Thread Stack Address Attribute
228 option. If this symbol is defined in <unistd.h>, it shall be
229 defined to be -1, 0, or 200809L. The value of this symbol
230 reported by sysconf() shall either be -1 or 200809L.
231 _POSIX_THREAD_ATTR_STACKSIZE
233 The implementation supports the Thread Stack Size Attribute
234 option. If this symbol is defined in <unistd.h>, it shall be
235 defined to be -1, 0, or 200809L. The value of this symbol
236 reported by sysconf() shall either be -1 or 200809L.
237 _POSIX_THREAD_CPUTIME
239 The implementation supports the Thread CPU-Time Clocks option.
240 If this symbol is defined in <unistd.h>, it shall be defined to
241 be -1, 0, or 200809L. The value of this symbol reported by
242 sysconf() shall either be -1 or 200809L.
243 _POSIX_THREAD_PRIO_INHERIT
245 The implementation supports the Non-Robust Mutex Priority Inheri‐
246 tance option. If this symbol is defined in <unistd.h>, it shall
247 be defined to be -1, 0, or 200809L. The value of this symbol
248 reported by sysconf() shall either be -1 or 200809L.
249 _POSIX_THREAD_PRIO_PROTECT
251 The implementation supports the Non-Robust Mutex Priority Protec‐
252 tion option. If this symbol is defined in <unistd.h>, it shall be
253 defined to be -1, 0, or 200809L. The value of this symbol
254 reported by sysconf() shall either be -1 or 200809L.
255 _POSIX_THREAD_PRIORITY_SCHEDULING
257 The implementation supports the Thread Execution Scheduling
258 option. If this symbol is defined in <unistd.h>, it shall be
259 defined to be -1, 0, or 200809L. The value of this symbol
260 reported by sysconf() shall either be -1 or 200809L.
261 _POSIX_THREAD_PROCESS_SHARED
263 The implementation supports the Thread Process-Shared Synchro‐
264 nization option. If this symbol is defined in <unistd.h>, it
265 shall be defined to be -1, 0, or 200809L. The value of this sym‐
266 bol reported by sysconf() shall either be -1 or 200809L.
267 _POSIX_THREAD_ROBUST_PRIO_INHERIT
269 The implementation supports the Robust Mutex Priority Inheritance
270 option. If this symbol is defined in <unistd.h>, it shall be
271 defined to be -1, 0, or 200809L. The value of this symbol
272 reported by sysconf() shall either be -1 or 200809L.
273 _POSIX_THREAD_ROBUST_PRIO_PROTECT
275 The implementation supports the Robust Mutex Priority Protection
276 option. If this symbol is defined in <unistd.h>, it shall be
277 defined to be -1, 0, or 200809L. The value of this symbol
278 reported by sysconf() shall either be -1 or 200809L.
279 _POSIX_THREAD_SAFE_FUNCTIONS
281 The implementation supports thread-safe functions. This symbol
282 shall always be set to the value 200809L.
283 _POSIX_THREAD_SPORADIC_SERVER
285 The implementation supports the Thread Sporadic Server option.
286 If this symbol is defined in <unistd.h>, it shall be defined to
287 be -1, 0, or 200809L. The value of this symbol reported by
288 sysconf() shall either be -1 or 200809L.
289 _POSIX_THREADS
291 The implementation supports threads. This symbol shall always be
292 set to the value 200809L.
293 _POSIX_TIMEOUTS
295 The implementation supports timeouts. This symbol shall always
296 be set to the value 200809L.
297 _POSIX_TIMERS
299 The implementation supports timers. This symbol shall always be
300 set to the value 200809L.
301 _POSIX_TRACE
303 The implementation supports the Trace option. If this symbol is
304 defined in <unistd.h>, it shall be defined to be -1, 0, or
305 200809L. The value of this symbol reported by sysconf() shall
306 either be -1 or 200809L.
307 _POSIX_TRACE_EVENT_FILTER
309 The implementation supports the Trace Event Filter option. If
310 this symbol is defined in <unistd.h>, it shall be defined to be
311 -1, 0, or 200809L. The value of this symbol reported by sysconf()
312 shall either be -1 or 200809L.
313 _POSIX_TRACE_INHERIT
315 The implementation supports the Trace Inherit option. If this
316 symbol is defined in <unistd.h>, it shall be defined to be -1, 0,
317 or 200809L. The value of this symbol reported by sysconf() shall
318 either be -1 or 200809L.
319 _POSIX_TRACE_LOG
321 The implementation supports the Trace Log option. If this symbol
322 is defined in <unistd.h>, it shall be defined to be -1, 0, or
323 200809L. The value of this symbol reported by sysconf() shall
324 either be -1 or 200809L.
325 _POSIX_TYPED_MEMORY_OBJECTS
327 The implementation supports the Typed Memory Objects option. If
328 this symbol is defined in <unistd.h>, it shall be defined to be
329 -1, 0, or 200809L. The value of this symbol reported by sysconf()
330 shall either be -1 or 200809L.
331 _POSIX_V6_ILP32_OFF32
333 The implementation provides a C-language compilation environment
334 with 32-bit int, long, pointer, and off_t types.
335 _POSIX_V6_ILP32_OFFBIG
337 The implementation provides a C-language compilation environment
338 with 32-bit int, long, and pointer types and an off_t type using
339 at least 64 bits.
340 _POSIX_V6_LP64_OFF64
342 The implementation provides a C-language compilation environment
343 with 32-bit int and 64-bit long, pointer, and off_t types.
344 _POSIX_V6_LPBIG_OFFBIG
346 The implementation provides a C-language compilation environment
347 with an int type using at least 32 bits and long, pointer, and
348 off_t types using at least 64 bits.
349 _POSIX_V7_ILP32_OFF32
351 The implementation provides a C-language compilation environment
352 with 32-bit int, long, pointer, and off_t types.
353 _POSIX_V7_ILP32_OFFBIG
355 The implementation provides a C-language compilation environment
356 with 32-bit int, long, and pointer types and an off_t type using
357 at least 64 bits.
358 _POSIX_V7_LP64_OFF64
360 The implementation provides a C-language compilation environment
361 with 32-bit int and 64-bit long, pointer, and off_t types.
362 _POSIX_V7_LPBIG_OFFBIG
364 The implementation provides a C-language compilation environment
365 with an int type using at least 32 bits and long, pointer, and
366 off_t types using at least 64 bits.
367 _POSIX2_C_BIND
369 The implementation supports the C-Language Binding option. This
370 symbol shall always have the value 200809L.
371 _POSIX2_C_DEV
373 The implementation supports the C-Language Development Utilities
374 option. If this symbol is defined in <unistd.h>, it shall be
375 defined to be -1, 0, or 200809L. The value of this symbol
376 reported by sysconf() shall either be -1 or 200809L.
377 _POSIX2_CHAR_TERM
379 The implementation supports the Terminal Characteristics option.
380 The value of this symbol reported by sysconf() shall either be -1
381 or a value greater than zero.
382 _POSIX2_FORT_DEV
384 The implementation supports the FORTRAN Development Utilities
385 option. If this symbol is defined in <unistd.h>, it shall be
386 defined to be -1, 0, or 200809L. The value of this symbol
387 reported by sysconf() shall either be -1 or 200809L.
388 _POSIX2_FORT_RUN
390 The implementation supports the FORTRAN Runtime Utilities option.
391 If this symbol is defined in <unistd.h>, it shall be defined to
392 be -1, 0, or 200809L. The value of this symbol reported by
393 sysconf() shall either be -1 or 200809L.
394 _POSIX2_LOCALEDEF
396 The implementation supports the creation of locales by the
397 localedef utility. If this symbol is defined in <unistd.h>, it
398 shall be defined to be -1, 0, or 200809L. The value of this sym‐
399 bol reported by sysconf() shall either be -1 or 200809L.
400 _POSIX2_PBS
402 The implementation supports the Batch Environment Services and
403 Utilities option. If this symbol is defined in <unistd.h>, it
404 shall be defined to be -1, 0, or 200809L. The value of this sym‐
405 bol reported by sysconf() shall either be -1 or 200809L.
406 _POSIX2_PBS_ACCOUNTING
408 The implementation supports the Batch Accounting option. If this
409 symbol is defined in <unistd.h>, it shall be defined to be -1, 0,
410 or 200809L. The value of this symbol reported by sysconf() shall
411 either be -1 or 200809L.
412 _POSIX2_PBS_CHECKPOINT
414 The implementation supports the Batch Checkpoint/Restart option.
415 If this symbol is defined in <unistd.h>, it shall be defined to
416 be -1, 0, or 200809L. The value of this symbol reported by
417 sysconf() shall either be -1 or 200809L.
418 _POSIX2_PBS_LOCATE
420 The implementation supports the Locate Batch Job Request option.
421 If this symbol is defined in <unistd.h>, it shall be defined to
422 be -1, 0, or 200809L. The value of this symbol reported by
423 sysconf() shall either be -1 or 200809L.
424 _POSIX2_PBS_MESSAGE
426 The implementation supports the Batch Job Message Request option.
427 If this symbol is defined in <unistd.h>, it shall be defined to
428 be -1, 0, or 200809L. The value of this symbol reported by
429 sysconf() shall either be -1 or 200809L.
430 _POSIX2_PBS_TRACK
432 The implementation supports the Track Batch Job Request option.
433 If this symbol is defined in <unistd.h>, it shall be defined to
434 be -1, 0, or 200809L. The value of this symbol reported by
435 sysconf() shall either be -1 or 200809L.
436 _POSIX2_SW_DEV
438 The implementation supports the Software Development Utilities
439 option. If this symbol is defined in <unistd.h>, it shall be
440 defined to be -1, 0, or 200809L. The value of this symbol
441 reported by sysconf() shall either be -1 or 200809L.
442 _POSIX2_UPE
444 The implementation supports the User Portability Utilities
445 option. If this symbol is defined in <unistd.h>, it shall be
446 defined to be -1, 0, or 200809L. The value of this symbol
447 reported by sysconf() shall either be -1 or 200809L.
448 _XOPEN_CRYPT
450 The implementation supports the X/Open Encryption Option Group.
451 _XOPEN_ENH_I18N
453 The implementation supports the Issue 4, Version 2 Enhanced
454 Internationalization Option Group. This symbol shall always be
455 set to a value other than -1.
456 _XOPEN_REALTIME
458 The implementation supports the X/Open Realtime Option Group.
459 _XOPEN_REALTIME_THREADS
461 The implementation supports the X/Open Realtime Threads Option
462 Group.
463 _XOPEN_SHM
465 The implementation supports the Issue 4, Version 2 Shared Memory
466 Option Group. This symbol shall always be set to a value other
467 than -1.
468 _XOPEN_STREAMS
470 The implementation supports the XSI STREAMS Option Group.
471 _XOPEN_UNIX
473 The implementation supports the XSI option.
474 _XOPEN_UUCP
476 The implementation supports the UUCP Utilities option. If this
477 symbol is defined in <unistd.h>, it shall be defined to be -1, 0,
478 or 200809L. The value of this symbol reported by sysconf() shall
479 be either -1 or 200809L.
480 Execution-Time Symbolic Constants
482 If any of the following symbolic constants are not defined in the
483 <unistd.h> header, the value shall vary depending on the file to which
484 it is applied. If defined, they shall have values suitable for use in
485 #if preprocessing directives.
486 If any of the following symbolic constants are defined to have value -1
488 in the <unistd.h> header, the implementation shall not provide the
489 option on any file; if any are defined to have a value other than -1 in
490 the <unistd.h> header, the implementation shall provide the option on
491 all applicable files.
492 All of the following values, whether defined as symbolic constants in
494 <unistd.h> or not, may be queried with respect to a specific file using
495 the pathconf() or fpathconf() functions:
496 _POSIX_ASYNC_IO
498 Asynchronous input or output operations may be performed for the
499 associated file.
500 _POSIX_PRIO_IO
502 Prioritized input or output operations may be performed for the
503 associated file.
504 _POSIX_SYNC_IO
506 Synchronized input or output operations may be performed for the
507 associated file.
508 If the following symbolic constants are defined in the <unistd.h>
510 header, they apply to files and all paths in all file systems on the
511 implementation:
512 _POSIX_TIMESTAMP_RESOLUTION
514 The resolution in nanoseconds for all file timestamps.
515 _POSIX2_SYMLINKS
517 Symbolic links can be created.
518 Constants for Functions
520 The <unistd.h> header shall define NULL as described in <stddef.h>.
521 The <unistd.h> header shall define the following symbolic constants for
523 use with the access() function. The values shall be suitable for use in
524 #if preprocessing directives.
525 F_OK Test for existence of file.
527 R_OK Test for read permission.
529 W_OK Test for write permission.
531 X_OK Test for execute (search) permission.
533 The constants F_OK, R_OK, W_OK, and X_OK and the expressions R_OK|W_OK,
535 R_OK|X_OK, and R_OK|W_OK|X_OK shall all have distinct values.
536 The <unistd.h> header shall define the following symbolic constants for
538 the confstr() function:
539 _CS_PATH
541 This is the value for the PATH environment variable that finds
542 all of the standard utilities that are provided in a manner
543 accessible via the exec family of functions.
544 _CS_POSIX_V7_ILP32_OFF32_CFLAGS
546 If sysconf(_SC_V7_ILP32_OFF32) returns -1, the meaning of this
547 value is unspecified. Otherwise, this value is the set of initial
548 options to be given to the c99 utility to build an application
549 using a programming model with 32-bit int, long, pointer, and
550 off_t types.
551 _CS_POSIX_V7_ILP32_OFF32_LDFLAGS
553 If sysconf(_SC_V7_ILP32_OFF32) returns -1, the meaning of this
554 value is unspecified. Otherwise, this value is the set of final
555 options to be given to the c99 utility to build an application
556 using a programming model with 32-bit int, long, pointer, and
557 off_t types.
558 _CS_POSIX_V7_ILP32_OFF32_LIBS
560 If sysconf(_SC_V7_ILP32_OFF32) returns -1, the meaning of this
561 value is unspecified. Otherwise, this value is the set of
562 libraries to be given to the c99 utility to build an application
563 using a programming model with 32-bit int, long, pointer, and
564 off_t types.
565 _CS_POSIX_V7_ILP32_OFFBIG_CFLAGS
567 If sysconf(_SC_V7_ILP32_OFFBIG) returns -1, the meaning of this
568 value is unspecified. Otherwise, this value is the set of initial
569 options to be given to the c99 utility to build an application
570 using a programming model with 32-bit int, long, and pointer
571 types, and an off_t type using at least 64 bits.
572 _CS_POSIX_V7_ILP32_OFFBIG_LDFLAGS
574 If sysconf(_SC_V7_ILP32_OFFBIG) returns -1, the meaning of this
575 value is unspecified. Otherwise, this value is the set of final
576 options to be given to the c99 utility to build an application
577 using a programming model with 32-bit int, long, and pointer
578 types, and an off_t type using at least 64 bits.
579 _CS_POSIX_V7_ILP32_OFFBIG_LIBS
581 If sysconf(_SC_V7_ILP32_OFFBIG) returns -1, the meaning of this
582 value is unspecified. Otherwise, this value is the set of
583 libraries to be given to the c99 utility to build an application
584 using a programming model with 32-bit int, long, and pointer
585 types, and an off_t type using at least 64 bits.
586 _CS_POSIX_V7_LP64_OFF64_CFLAGS
588 If sysconf(_SC_V7_LP64_OFF64) returns -1, the meaning of this
589 value is unspecified. Otherwise, this value is the set of initial
590 options to be given to the c99 utility to build an application
591 using a programming model with 32-bit int and 64-bit long,
592 pointer, and off_t types.
593 _CS_POSIX_V7_LP64_OFF64_LDFLAGS
595 If sysconf(_SC_V7_LP64_OFF64) returns -1, the meaning of this
596 value is unspecified. Otherwise, this value is the set of final
597 options to be given to the c99 utility to build an application
598 using a programming model with 32-bit int and 64-bit long,
599 pointer, and off_t types.
600 _CS_POSIX_V7_LP64_OFF64_LIBS
602 If sysconf(_SC_V7_LP64_OFF64) returns -1, the meaning of this
603 value is unspecified. Otherwise, this value is the set of
604 libraries to be given to the c99 utility to build an application
605 using a programming model with 32-bit int and 64-bit long,
606 pointer, and off_t types.
607 _CS_POSIX_V7_LPBIG_OFFBIG_CFLAGS
609 If sysconf(_SC_V7_LPBIG_OFFBIG) returns -1, the meaning of this
610 value is unspecified. Otherwise, this value is the set of initial
611 options to be given to the c99 utility to build an application
612 using a programming model with an int type using at least 32 bits
613 and long, pointer, and off_t types using at least 64 bits.
614 _CS_POSIX_V7_LPBIG_OFFBIG_LDFLAGS
616 If sysconf(_SC_V7_LPBIG_OFFBIG) returns -1, the meaning of this
617 value is unspecified. Otherwise, this value is the set of final
618 options to be given to the c99 utility to build an application
619 using a programming model with an int type using at least 32 bits
620 and long, pointer, and off_t types using at least 64 bits.
621 _CS_POSIX_V7_LPBIG_OFFBIG_LIBS
623 If sysconf(_SC_V7_LPBIG_OFFBIG) returns -1, the meaning of this
624 value is unspecified. Otherwise, this value is the set of
625 libraries to be given to the c99 utility to build an application
626 using a programming model with an int type using at least 32 bits
627 and long, pointer, and off_t types using at least 64 bits.
628 _CS_POSIX_V7_THREADS_CFLAGS
630 If sysconf(_SC_POSIX_THREADS) returns -1, the meaning of this
631 value is unspecified. Otherwise, this value is the set of initial
632 options to be given to the c99 utility to build a multi-threaded
633 application. These flags are in addition to those associated with
634 any of the other _CS_POSIX_V7_*_CFLAGS values used to specify
635 particular type size programing environments.
636 _CS_POSIX_V7_THREADS_LDFLAGS
638 If sysconf(_SC_POSIX_THREADS) returns -1, the meaning of this
639 value is unspecified. Otherwise, this value is the set of final
640 options to be given to the c99 utility to build a multi-threaded
641 application. These flags are in addition to those associated with
642 any of the other _CS_POSIX_V7_*_LDFLAGS values used to specify
643 particular type size programing environments.
644 _CS_POSIX_V7_WIDTH_RESTRICTED_ENVS
646 This value is a <newline>-separated list of names of programming
647 environments supported by the implementation in which the widths
648 of the blksize_t, cc_t, mode_t, nfds_t, pid_t, ptrdiff_t, size_t,
649 speed_t, ssize_t, suseconds_t, tcflag_t, wchar_t, and wint_t
650 types are no greater than the width of type long. The format of
651 each name shall be suitable for use with the getconf -v option.
652 _CS_V7_ENV
654 This is the value that provides the environment variable informa‐
655 tion (other than that provided by _CS_PATH) that is required by
656 the implementation to create a conforming environment, as
657 described in the implementation's conformance documentation.
658 The following symbolic constants are reserved for compatibility with
660 Issue 6:
661 _CS_POSIX_V6_ILP32_OFF32_CFLAGS
663 _CS_POSIX_V6_ILP32_OFF32_LDFLAGS
664 _CS_POSIX_V6_ILP32_OFF32_LIBS
665 _CS_POSIX_V6_ILP32_OFFBIG_CFLAGS
666 _CS_POSIX_V6_ILP32_OFFBIG_LDFLAGS
667 _CS_POSIX_V6_ILP32_OFFBIG_LIBS
668 _CS_POSIX_V6_LP64_OFF64_CFLAGS
669 _CS_POSIX_V6_LP64_OFF64_LDFLAGS
670 _CS_POSIX_V6_LP64_OFF64_LIBS
671 _CS_POSIX_V6_LPBIG_OFFBIG_CFLAGS
672 _CS_POSIX_V6_LPBIG_OFFBIG_LDFLAGS
673 _CS_POSIX_V6_LPBIG_OFFBIG_LIBS
674 _CS_POSIX_V6_WIDTH_RESTRICTED_ENVS
675 _CS_V6_ENV
676 The <unistd.h> header shall define SEEK_CUR, SEEK_END, and SEEK_SET as
678 described in <stdio.h>.
679 The <unistd.h> header shall define the following symbolic constants as
681 possible values for the function argument to the lockf() function:
682 F_LOCK Lock a section for exclusive use.
684 F_TEST Test section for locks by other processes.
686 F_TLOCK Test and lock a section for exclusive use.
688 F_ULOCK Unlock locked sections.
690 The <unistd.h> header shall define the following symbolic constants for
692 pathconf():
693 _PC_2_SYMLINKS
695 _PC_ALLOC_SIZE_MIN
696 _PC_ASYNC_IO
697 _PC_CHOWN_RESTRICTED
698 _PC_FILESIZEBITS
699 _PC_LINK_MAX
700 _PC_MAX_CANON
701 _PC_MAX_INPUT
702 _PC_NAME_MAX
703 _PC_NO_TRUNC
704 _PC_PATH_MAX
705 _PC_PIPE_BUF
706 _PC_PRIO_IO
707 _PC_REC_INCR_XFER_SIZE
708 _PC_REC_MAX_XFER_SIZE
709 _PC_REC_MIN_XFER_SIZE
710 _PC_REC_XFER_ALIGN
711 _PC_SYMLINK_MAX
712 _PC_SYNC_IO
713 _PC_TIMESTAMP_RESOLUTION
714 _PC_VDISABLE
715 The <unistd.h> header shall define the following symbolic constants for
717 sysconf():
718 _SC_2_C_BIND
720 _SC_2_C_DEV
721 _SC_2_CHAR_TERM
722 _SC_2_FORT_DEV
723 _SC_2_FORT_RUN
724 _SC_2_LOCALEDEF
725 _SC_2_PBS
726 _SC_2_PBS_ACCOUNTING
727 _SC_2_PBS_CHECKPOINT
728 _SC_2_PBS_LOCATE
729 _SC_2_PBS_MESSAGE
730 _SC_2_PBS_TRACK
731 _SC_2_SW_DEV
732 _SC_2_UPE
733 _SC_2_VERSION
734 _SC_ADVISORY_INFO
735 _SC_AIO_LISTIO_MAX
736 _SC_AIO_MAX
737 _SC_AIO_PRIO_DELTA_MAX
738 _SC_ARG_MAX
739 _SC_ASYNCHRONOUS_IO
740 _SC_ATEXIT_MAX
741 _SC_BARRIERS
742 _SC_BC_BASE_MAX
743 _SC_BC_DIM_MAX
744 _SC_BC_SCALE_MAX
745 _SC_BC_STRING_MAX
746 _SC_CHILD_MAX
747 _SC_CLK_TCK
748 _SC_CLOCK_SELECTION
749 _SC_COLL_WEIGHTS_MAX
750 _SC_CPUTIME
751 _SC_DELAYTIMER_MAX
752 _SC_EXPR_NEST_MAX
753 _SC_FSYNC
754 _SC_GETGR_R_SIZE_MAX
755 _SC_GETPW_R_SIZE_MAX
756 _SC_HOST_NAME_MAX
757 _SC_IOV_MAX
758 _SC_IPV6
759 _SC_JOB_CONTROL
760 _SC_LINE_MAX
761 _SC_LOGIN_NAME_MAX
762 _SC_MAPPED_FILES
763 _SC_MEMLOCK
764 _SC_MEMLOCK_RANGE
765 _SC_MEMORY_PROTECTION
766 _SC_MESSAGE_PASSING
767 _SC_MONOTONIC_CLOCK
768 _SC_MQ_OPEN_MAX
769 _SC_MQ_PRIO_MAX
770 _SC_NGROUPS_MAX
771 _SC_OPEN_MAX
772 _SC_PAGE_SIZE
773 _SC_PAGESIZE
774 _SC_PRIORITIZED_IO
775 _SC_PRIORITY_SCHEDULING
776 _SC_RAW_SOCKETS
777 _SC_RE_DUP_MAX
778 _SC_READER_WRITER_LOCKS
779 _SC_REALTIME_SIGNALS
780 _SC_REGEXP
781 _SC_RTSIG_MAX
782 _SC_SAVED_IDS
783 _SC_SEM_NSEMS_MAX
784 _SC_SEM_VALUE_MAX
785 _SC_SEMAPHORES
786 _SC_SHARED_MEMORY_OBJECTS
787 _SC_SHELL
788 _SC_SIGQUEUE_MAX
789 _SC_SPAWN
790 _SC_SPIN_LOCKS
791 _SC_SPORADIC_SERVER
792 _SC_SS_REPL_MAX
793 _SC_STREAM_MAX
794 _SC_SYMLOOP_MAX
795 _SC_SYNCHRONIZED_IO
796 _SC_THREAD_ATTR_STACKADDR
797 _SC_THREAD_ATTR_STACKSIZE
798 _SC_THREAD_CPUTIME
799 _SC_THREAD_DESTRUCTOR_ITERATIONS
800 _SC_THREAD_KEYS_MAX
801 _SC_THREAD_PRIO_INHERIT
802 _SC_THREAD_PRIO_PROTECT
803 _SC_THREAD_PRIORITY_SCHEDULING
804 _SC_THREAD_PROCESS_SHARED
805 _SC_THREAD_ROBUST_PRIO_INHERIT
806 _SC_THREAD_ROBUST_PRIO_PROTECT
807 _SC_THREAD_SAFE_FUNCTIONS
808 _SC_THREAD_SPORADIC_SERVER
809 _SC_THREAD_STACK_MIN
810 _SC_THREAD_THREADS_MAX
811 _SC_THREADS
812 _SC_TIMEOUTS
813 _SC_TIMER_MAX
814 _SC_TIMERS
815 _SC_TRACE
816 _SC_TRACE_EVENT_FILTER
817 _SC_TRACE_EVENT_NAME_MAX
818 _SC_TRACE_INHERIT
819 _SC_TRACE_LOG
820 _SC_TRACE_NAME_MAX
821 _SC_TRACE_SYS_MAX
822 _SC_TRACE_USER_EVENT_MAX
823 _SC_TTY_NAME_MAX
824 _SC_TYPED_MEMORY_OBJECTS
825 _SC_TZNAME_MAX
826 _SC_V7_ILP32_OFF32
827 _SC_V7_ILP32_OFFBIG
828 _SC_V7_LP64_OFF64
829 _SC_V7_LPBIG_OFFBIG
830 _SC_V6_ILP32_OFF32
831 _SC_V6_ILP32_OFFBIG
832 _SC_V6_LP64_OFF64
833 _SC_V6_LPBIG_OFFBIG
834 _SC_VERSION
835 _SC_XOPEN_CRYPT
836 _SC_XOPEN_ENH_I18N
837 _SC_XOPEN_REALTIME
838 _SC_XOPEN_REALTIME_THREADS
839 _SC_XOPEN_SHM
840 _SC_XOPEN_STREAMS
841 _SC_XOPEN_UNIX
842 _SC_XOPEN_UUCP
843 _SC_XOPEN_VERSION
844 The two constants _SC_PAGESIZE and _SC_PAGE_SIZE may be defined to have
846 the same value.
847 The <unistd.h> header shall define the following symbolic constants for
849 file streams:
850 STDERR_FILENO File number of stderr; 2.
852 STDIN_FILENO File number of stdin; 0.
854 STDOUT_FILENO File number of stdout; 1.
856 The <unistd.h> header shall define the following symbolic constant for
858 terminal special character handling:
859 _POSIX_VDISABLE
861 This symbol shall be defined to be the value of a charac‐
862 ter that shall disable terminal special character han‐
863 dling as described in Section 11.2.6, Special Control
864 Characters. This symbol shall always be set to a value
865 other than -1.
866 Type Definitions
868 The <unistd.h> header shall define the size_t, ssize_t, uid_t, gid_t,
869 off_t, and pid_t types as described in <sys/types.h>.
870 The <unistd.h> header shall define the intptr_t type as described in
872 <stdint.h>.
873 Declarations
875 The following shall be declared as functions and may also be defined as
876 macros. Function prototypes shall be provided.
877 int access(const char *, int);
880 unsigned alarm(unsigned);
881 int chdir(const char *);
882 int chown(const char *, uid_t, gid_t);
883 int close(int);
884 size_t confstr(int, char *, size_t);
885 char *crypt(const char *, const char *);
886 int dup(int);
887 int dup2(int, int);
888 void _exit(int);
889 void encrypt(char [64], int);
890 int execl(const char *, const char *, ...);
891 int execle(const char *, const char *, ...);
892 int execlp(const char *, const char *, ...);
893 int execv(const char *, char *const []);
894 int execve(const char *, char *const [], char *const []);
895 int execvp(const char *, char *const []);
896 int faccessat(int, const char *, int, int);
897 int fchdir(int);
898 int fchown(int, uid_t, gid_t);
899 int fchownat(int, const char *, uid_t, gid_t, int);
900 int fdatasync(int);
901 int fexecve(int, char *const [], char *const []);
902 pid_t fork(void);
903 long fpathconf(int, int);
904 int fsync(int);
905 int ftruncate(int, off_t);
906 char *getcwd(char *, size_t);
907 gid_t getegid(void);
908 uid_t geteuid(void);
909 gid_t getgid(void);
910 int getgroups(int, gid_t []);
911 long gethostid(void);
912 int gethostname(char *, size_t);
913 char *getlogin(void);
914 int getlogin_r(char *, size_t);
915 int getopt(int, char * const [], const char *);
916 pid_t getpgid(pid_t);
917 pid_t getpgrp(void);
918 pid_t getpid(void);
919 pid_t getppid(void);
920 pid_t getsid(pid_t);
921 uid_t getuid(void);
922 int isatty(int);
923 int lchown(const char *, uid_t, gid_t);
924 int link(const char *, const char *);
925 int linkat(int, const char *, int, const char *, int);
926 int lockf(int, int, off_t);
927 off_t lseek(int, off_t, int);
928 int nice(int);
929 long pathconf(const char *, int);
930 int pause(void);
931 int pipe(int [2]);
932 ssize_t pread(int, void *, size_t, off_t);
933 ssize_t pwrite(int, const void *, size_t, off_t);
934 ssize_t read(int, void *, size_t);
935 ssize_t readlink(const char *restrict, char *restrict, size_t);
936 ssize_t readlinkat(int, const char *restrict, char *restrict, size_t);
937 int rmdir(const char *);
938 int setegid(gid_t);
939 int seteuid(uid_t);
940 int setgid(gid_t);
941 int setpgid(pid_t, pid_t);
942 pid_t setpgrp(void);
943 int setregid(gid_t, gid_t);
944 int setreuid(uid_t, uid_t);
945 pid_t setsid(void);
946 int setuid(uid_t);
947 unsigned sleep(unsigned);
948 void swab(const void *restrict, void *restrict, ssize_t);
949 int symlink(const char *, const char *);
950 int symlinkat(const char *, int, const char *);
951 void sync(void);
952 long sysconf(int);
953 pid_t tcgetpgrp(int);
954 int tcsetpgrp(int, pid_t);
955 int truncate(const char *, off_t);
956 char *ttyname(int);
957 int ttyname_r(int, char *, size_t);
958 int unlink(const char *);
959 int unlinkat(int, const char *, int);
960 ssize_t write(int, const void *, size_t);
961 Implementations may also include the pthread_atfork() prototype as
963 defined in <pthread.h>. Implementations may also include the ctermid()
964 prototype as defined in <stdio.h>.
965 The <unistd.h> header shall declare the following external variables:
967 extern char *optarg;
970 extern int opterr, optind, optopt;
971 Inclusion of the <unistd.h> header may make visible all symbols from
973 the headers <stddef.h>, <stdint.h>, and <stdio.h>.
974 The following sections are informative.
976
978 POSIX.1‐2008 only describes the behavior of systems that claim confor‐
979 mance to it. However, application developers who want to write applica‐
980 tions that adapt to other versions of this standard (or to systems that
981 do not conform to any POSIX standard) may find it useful to code them
982 so as to conditionally compile different code depending on the value of
983 _POSIX_VERSION, for example:
984 #if _POSIX_VERSION >= 200112L
987 /* Use the newer function that copes with large files. */
988 off_t pos=ftello(fp);
989 #else
990 /* Either this is an old version of POSIX, or _POSIX_VERSION is
991 not even defined, so use the traditional function. */
992 long pos=ftell(fp);
993 #endif
994 Earlier versions of POSIX.1‐2008 and of the Single UNIX Specification
996 can be identified by the following macros:
997 POSIX.1‐1988 standard
999 _POSIX_VERSION==198808L
1000 POSIX.1‐1990 standard
1002 _POSIX_VERSION==199009L
1003 ISO POSIX‐1:1996 standard
1005 _POSIX_VERSION==199506L
1006 Single UNIX Specification, Version 1
1008 _XOPEN_UNIX and _XOPEN_VERSION==4
1009 Single UNIX Specification, Version 2
1011 _XOPEN_UNIX and _XOPEN_VERSION==500
1012 ISO POSIX‐1:2001 and Single UNIX Specification, Version 3
1014 _POSIX_VERSION==200112L, plus (if the XSI option is supported)
1015 _XOPEN_UNIX and _XOPEN_VERSION==600
1016 POSIX.1‐2008 does not make any attempt to define application binary
1018 interaction with the underlying operating system. However, application
1019 developers may find it useful to query _SC_VERSION at runtime via
1020 sysconf() to determine whether the current version of the operating
1021 system supports the necessary functionality as in the following program
1022 fragment:
1023 if (sysconf(_SC_VERSION) < 200809L) {
1026 fprintf(stderr, "POSIX.1-2008 system required, terminating \n");
1027 exit(1);
1028 }
1029 New applications should not use _XOPEN_SHM or _XOPEN_ENH_I18N.
1031
1033 As POSIX.1‐2008 evolved, certain options became sufficiently standard‐
1034 ized that it was concluded that simply requiring one of the option
1035 choices was simpler than retaining the option. However, for backwards-
1036 compatibility, the option flags (with required constant values) are
1037 retained.
1038 Version Test Macros
1040 The standard developers considered altering the definition of
1041 _POSIX_VERSION and removing _SC_VERSION from the specification of
1042 sysconf() since the utility to an application was deemed by some to be
1043 minimal, and since the implementation of the functionality is poten‐
1044 tially problematic. However, they recognized that support for existing
1045 application binaries is a concern to manufacturers, application devel‐
1046 opers, and the users of implementations conforming to POSIX.1‐2008.
1047 While the example using _SC_VERSION in the APPLICATION USAGE section
1049 does not provide the greatest degree of imaginable utility to the
1050 application developer or user, it is arguably better than a core file
1051 or some other equally obscure result. (It is also possible for imple‐
1052 mentations to encode and recognize application binaries compiled in
1053 various POSIX.1-conforming environments, and modify the semantics of
1054 the underlying system to conform to the expectations of the applica‐
1055 tion.) For the reasons outlined in the preceding paragraphs and in the
1056 APPLICATION USAGE section, the standard developers elected to retain
1057 the _POSIX_VERSION and _SC_VERSION functionality.
1058 Compile-Time Symbolic Constants for System-Wide Options
1060 POSIX.1‐2008 includes support in certain areas for the newly adopted
1061 policy governing options and stubs.
1062 This policy provides flexibility for implementations in how they sup‐
1064 port options. It also specifies how conforming applications can adapt
1065 to different implementations that support different sets of options. It
1066 allows the following:
1067 1. If an implementation has no interest in supporting an option, it
1069 does not have to provide anything associated with that option
1070 beyond the announcement that it does not support it.
1071 2. An implementation can support a partial or incompatible version of
1073 an option (as a non-standard extension) as long as it does not
1074 claim to support the option.
1075 3. An application can determine whether the option is supported. A
1077 strictly conforming application must check this announcement mecha‐
1078 nism before first using anything associated with the option.
1079 There is an important implication of this policy. POSIX.1‐2008 cannot
1081 dictate the behavior of interfaces associated with an option when the
1082 implementation does not claim to support the option. In particular, it
1083 cannot require that a function associated with an unsupported option
1084 will fail if it does not perform as specified. However, this policy
1085 does not prevent a standard from requiring certain functions to always
1086 be present, but that they shall always fail on some implementations.
1087 The setpgid() function in the POSIX.1‐1990 standard, for example, is
1088 considered appropriate.
1089 The POSIX standards include various options, and the C-language binding
1091 support for an option implies that the implementation must supply data
1092 types and function interfaces. An application must be able to discover
1093 whether the implementation supports each option.
1094 Any application must consider the following three cases for each
1096 option:
1097 1. Option never supported.
1099 The implementation advertises at compile time that the option will
1101 never be supported. In this case, it is not necessary for the
1102 implementation to supply any of the data types or function inter‐
1103 faces that are provided only as part of the option. The implementa‐
1104 tion might provide data types and functions that are similar to
1105 those defined by POSIX.1‐2008, but there is no guarantee for any
1106 particular behavior.
1107 2. Option always supported.
1109 The implementation advertises at compile time that the option will
1111 always be supported. In this case, all data types and function
1112 interfaces shall be available and shall operate as specified.
1113 3. Option might or might not be supported.
1115 Some implementations might not provide a mechanism to specify sup‐
1117 port of options at compile time. In addition, the implementation
1118 might be unable or unwilling to specify support or non-support at
1119 compile time. In either case, any application that might use the
1120 option at runtime must be able to compile and execute. The imple‐
1121 mentation must provide, at compile time, all data types and func‐
1122 tion interfaces that are necessary to allow this. In this situa‐
1123 tion, there must be a mechanism that allows the application to
1124 query, at runtime, whether the option is supported. If the applica‐
1125 tion attempts to use the option when it is not supported, the
1126 result is unspecified unless explicitly specified otherwise in
1127 POSIX.1‐2008.
1128
1130 None.
1131
1133 <limits.h>, <stddef.h>, <stdint.h>, <stdio.h>, <sys_socket.h>,
1134 <sys_types.h>, <termios.h>, <wctype.h>
1135 The System Interfaces volume of POSIX.1‐2017, access(), alarm(),
1137 chown(), close(), confstr(), crypt(), ctermid(), dup(), _Exit(),
1138 encrypt(), exec, fchdir(), fchown(), fdatasync(), fork(), fpathconf(),
1139 fsync(), ftruncate(), getcwd(), getegid(), geteuid(), getgid(), get‐
1140 groups(), gethostid(), gethostname(), getlogin(), getopt(), getpgid(),
1141 getpgrp(), getpid(), getppid(), getsid(), getuid(), isatty(), lchown(),
1142 link(), lockf(), lseek(), nice(), pause(), pipe(), read(), readlink(),
1143 rmdir(), setegid(), seteuid(), setgid(), setpgid(), setpgrp(),
1144 setregid(), setreuid(), setsid(), setuid(), sleep(), swab(), symlink(),
1145 sync(), sysconf(), tcgetpgrp(), tcsetpgrp(), truncate(), ttyname(),
1146 unlink(), write()
1147
1149 Portions of this text are reprinted and reproduced in electronic form
1150 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
1151 table Operating System Interface (POSIX), The Open Group Base Specifi‐
1152 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
1153 Electrical and Electronics Engineers, Inc and The Open Group. In the
1154 event of any discrepancy between this version and the original IEEE and
1155 The Open Group Standard, the original IEEE and The Open Group Standard
1156 is the referee document. The original Standard can be obtained online
1157 at http://www.opengroup.org/unix/online.html .
1158 Any typographical or formatting errors that appear in this page are
1160 most likely to have been introduced during the conversion of the source
1161 files to man page format. To report such errors, see https://www.ker‐
1162 nel.org/doc/man-pages/reporting_bugs.html .
1163IEEE/The Open Group 2017 unistd.h(0P)