1SYSCONF(3P) POSIX Programmer's Manual SYSCONF(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 sysconf - get configurable system variables
13
15 #include <unistd.h>
16 long sysconf(int name);
18
21 The sysconf() function provides a method for the application to deter‐
22 mine the current value of a configurable system limit or option ( vari‐
23 able). The implementation shall support all of the variables listed in
24 the following table and may support others.
25 The name argument represents the system variable to be queried. The
27 following table lists the minimal set of system variables from <lim‐
28 its.h> or <unistd.h> that can be returned by sysconf(), and the sym‐
29 bolic constants defined in <unistd.h> that are the corresponding values
30 used for name.
31 Variable Value of Name
33 {AIO_LISTIO_MAX} _SC_AIO_LISTIO_MAX
34 {AIO_MAX} _SC_AIO_MAX
35 {AIO_PRIO_DELTA_MAX} _SC_AIO_PRIO_DELTA_MAX
36 {ARG_MAX} _SC_ARG_MAX
37 {ATEXIT_MAX} _SC_ATEXIT_MAX
38 {BC_BASE_MAX} _SC_BC_BASE_MAX
39 {BC_DIM_MAX} _SC_BC_DIM_MAX
40 {BC_SCALE_MAX} _SC_BC_SCALE_MAX
41 {BC_STRING_MAX} _SC_BC_STRING_MAX
42 {CHILD_MAX} _SC_CHILD_MAX
43 Clock ticks/second _SC_CLK_TCK
44 {COLL_WEIGHTS_MAX} _SC_COLL_WEIGHTS_MAX
45 {DELAYTIMER_MAX} _SC_DELAYTIMER_MAX
46 {EXPR_NEST_MAX} _SC_EXPR_NEST_MAX
47 {HOST_NAME_MAX} _SC_HOST_NAME_MAX
48 {IOV_MAX} _SC_IOV_MAX
49 {LINE_MAX} _SC_LINE_MAX
50 {LOGIN_NAME_MAX} _SC_LOGIN_NAME_MAX
51 {NGROUPS_MAX} _SC_NGROUPS_MAX
52 Maximum size of getgrgid_r() and _SC_GETGR_R_SIZE_MAX
53 getgrnam_r() data buffers
54 Maximum size of getpwuid_r() and _SC_GETPW_R_SIZE_MAX
55 getpwnam_r() data buffers
56 {MQ_OPEN_MAX} _SC_MQ_OPEN_MAX
57 {MQ_PRIO_MAX} _SC_MQ_PRIO_MAX
58 {OPEN_MAX} _SC_OPEN_MAX
59 _POSIX_ADVISORY_INFO _SC_ADVISORY_INFO
60 _POSIX_BARRIERS _SC_BARRIERS
61 _POSIX_ASYNCHRONOUS_IO _SC_ASYNCHRONOUS_IO
62 _POSIX_CLOCK_SELECTION _SC_CLOCK_SELECTION
63 _POSIX_CPUTIME _SC_CPUTIME
64 _POSIX_FILE_LOCKING _SC_FILE_LOCKING
65 _POSIX_FSYNC _SC_FSYNC
66 _POSIX_IPV6 _SC_IPV6
68 _POSIX_JOB_CONTROL _SC_JOB_CONTROL
69 _POSIX_MAPPED_FILES _SC_MAPPED_FILES
70 _POSIX_MEMLOCK _SC_MEMLOCK
71 _POSIX_MEMLOCK_RANGE _SC_MEMLOCK_RANGE
72 _POSIX_MEMORY_PROTECTION _SC_MEMORY_PROTECTION
73 _POSIX_MESSAGE_PASSING _SC_MESSAGE_PASSING
74 _POSIX_MONOTONIC_CLOCK _SC_MONOTONIC_CLOCK
75 _POSIX_MULTI_PROCESS _SC_MULTI_PROCESS
76 _POSIX_PRIORITIZED_IO _SC_PRIORITIZED_IO
77 _POSIX_PRIORITY_SCHEDULING _SC_PRIORITY_SCHEDULING
78 _POSIX_RAW_SOCKETS _SC_RAW_SOCKETS
79 _POSIX_READER_WRITER_LOCKS _SC_READER_WRITER_LOCKS
80 _POSIX_REALTIME_SIGNALS _SC_REALTIME_SIGNALS
81 _POSIX_REGEXP _SC_REGEXP
82 _POSIX_SAVED_IDS _SC_SAVED_IDS
83 _POSIX_SEMAPHORES _SC_SEMAPHORES
84 _POSIX_SHARED_MEMORY_OBJECTS _SC_SHARED_MEMORY_OBJECTS
85 _POSIX_SHELL _SC_SHELL
86 _POSIX_SPAWN _SC_SPAWN
87 _POSIX_SPIN_LOCKS _SC_SPIN_LOCKS
88 _POSIX_SPORADIC_SERVER _SC_SPORADIC_SERVER
89 _POSIX_SYMLOOP_MAX _SC_SYMLOOP_MAX
90 _POSIX_SYNCHRONIZED_IO _SC_SYNCHRONIZED_IO
91 _POSIX_THREAD_ATTR_STACKADDR _SC_THREAD_ATTR_STACKADDR
92 _POSIX_THREAD_ATTR_STACKSIZE _SC_THREAD_ATTR_STACKSIZE
93 _POSIX_THREAD_CPUTIME _SC_THREAD_CPUTIME
94 _POSIX_THREAD_PRIO_INHERIT _SC_THREAD_PRIO_INHERIT
95 _POSIX_THREAD_PRIO_PROTECT _SC_THREAD_PRIO_PROTECT
96 _POSIX_THREAD_PRIORITY_SCHEDULING _SC_THREAD_PRIORITY_SCHEDULING
97 _POSIX_THREAD_PROCESS_SHARED _SC_THREAD_PROCESS_SHARED
98 _POSIX_THREAD_SAFE_FUNCTIONS _SC_THREAD_SAFE_FUNCTIONS
99 _POSIX_THREAD_SPORADIC_SERVER _SC_THREAD_SPORADIC_SERVER
100 _POSIX_THREADS _SC_THREADS
101 _POSIX_TIMEOUTS _SC_TIMEOUTS
102 _POSIX_TIMERS _SC_TIMERS
103 _POSIX_TRACE _SC_TRACE
104 _POSIX_TRACE_EVENT_FILTER _SC_TRACE_EVENT_FILTER
105 _POSIX_TRACE_INHERIT _SC_TRACE_INHERIT
106 _POSIX_TRACE_LOG _SC_TRACE_LOG
107 _POSIX_TYPED_MEMORY_OBJECTS _SC_TYPED_MEMORY_OBJECTS
108 _POSIX_VERSION _SC_VERSION
109 _POSIX_V6_ILP32_OFF32 _SC_V6_ILP32_OFF32
110 _POSIX_V6_ILP32_OFFBIG _SC_V6_ILP32_OFFBIG
111 _POSIX_V6_LP64_OFF64 _SC_V6_LP64_OFF64
112 _POSIX_V6_LPBIG_OFFBIG _SC_V6_LPBIG_OFFBIG
113 _POSIX2_C_BIND _SC_2_C_BIND
114 _POSIX2_C_DEV _SC_2_C_DEV
115 _POSIX2_C_VERSION _SC_2_C_VERSION
116 _POSIX2_CHAR_TERM _SC_2_CHAR_TERM
117 _POSIX2_FORT_DEV _SC_2_FORT_DEV
118 _POSIX2_FORT_RUN _SC_2_FORT_RUN
119 _POSIX2_LOCALEDEF _SC_2_LOCALEDEF
120 _POSIX2_PBS _SC_2_PBS
121 _POSIX2_PBS_ACCOUNTING _SC_2_PBS_ACCOUNTING
122 _POSIX2_PBS_CHECKPOINT _SC_2_PBS_CHECKPOINT
123 _POSIX2_PBS_LOCATE _SC_2_PBS_LOCATE
124 _POSIX2_PBS_MESSAGE _SC_2_PBS_MESSAGE
125 _POSIX2_PBS_TRACK _SC_2_PBS_TRACK
126 _POSIX2_SW_DEV _SC_2_SW_DEV
127 _POSIX2_UPE _SC_2_UPE
128 _POSIX2_VERSION _SC_2_VERSION
129 _REGEX_VERSION _SC_REGEX_VERSION
130 {PAGE_SIZE} _SC_PAGE_SIZE
131 {PAGESIZE} _SC_PAGESIZE
132 {PTHREAD_DESTRUCTOR_ITERATIONS} _SC_THREAD_DESTRUCTOR_ITERATIONS
134 {PTHREAD_KEYS_MAX} _SC_THREAD_KEYS_MAX
135 {PTHREAD_STACK_MIN} _SC_THREAD_STACK_MIN
136 {PTHREAD_THREADS_MAX} _SC_THREAD_THREADS_MAX
137 {RE_DUP_MAX} _SC_RE_DUP_MAX
138 {RTSIG_MAX} _SC_RTSIG_MAX
139 {SEM_NSEMS_MAX} _SC_SEM_NSEMS_MAX
140 {SEM_VALUE_MAX} _SC_SEM_VALUE_MAX
141 {SIGQUEUE_MAX} _SC_SIGQUEUE_MAX
142 {STREAM_MAX} _SC_STREAM_MAX
143 {SYMLOOP_MAX} _SC_SYMLOOP_MAX
144 {TIMER_MAX} _SC_TIMER_MAX
145 {TTY_NAME_MAX} _SC_TTY_NAME_MAX
146 {TZNAME_MAX} _SC_TZNAME_MAX
147 _XBS5_ILP32_OFF32 (LEGACY) _SC_XBS5_ILP32_OFF32 (LEGACY)
148 _XBS5_ILP32_OFFBIG (LEGACY) _SC_XBS5_ILP32_OFFBIG (LEGACY)
149 _XBS5_LP64_OFF64 (LEGACY) _SC_XBS5_LP64_OFF64 (LEGACY)
150 _XBS5_LPBIG_OFFBIG (LEGACY) _SC_XBS5_LPBIG_OFFBIG (LEGACY)
151 _XOPEN_CRYPT _SC_XOPEN_CRYPT
152 _XOPEN_ENH_I18N _SC_XOPEN_ENH_I18N
153 _XOPEN_LEGACY _SC_XOPEN_LEGACY
154 _XOPEN_REALTIME _SC_XOPEN_REALTIME
155 _XOPEN_REALTIME_THREADS _SC_XOPEN_REALTIME_THREADS
156 _XOPEN_SHM _SC_XOPEN_SHM
157 _XOPEN_STREAMS _SC_XOPEN_STREAMS
158 _XOPEN_UNIX _SC_XOPEN_UNIX
159 _XOPEN_VERSION _SC_XOPEN_VERSION
160 _XOPEN_XCU_VERSION _SC_XOPEN_XCU_VERSION
161
163 If name is an invalid value, sysconf() shall return -1 and set errno to
164 indicate the error. If the variable corresponding to name has no limit,
165 sysconf() shall return -1 without changing the value of errno. Note
166 that indefinite limits do not imply infinite limits; see <limits.h>.
167 Otherwise, sysconf() shall return the current variable value on the
169 system. The value returned shall not be more restrictive than the cor‐
170 responding value described to the application when it was compiled with
171 the implementation's <limits.h> or <unistd.h>. The value shall not
172 change during the lifetime of the calling process, except that
173 sysconf(_SC_OPEN_MAX) may return different values before and after a
174 call to setrlimit() which changes the RLIMIT_NOFILE soft limit.
175
177 The sysconf() function shall fail if:
178 EINVAL The value of the name argument is invalid.
180 The following sections are informative.
183
185 None.
186
188 As -1 is a permissible return value in a successful situation, an
189 application wishing to check for error situations should set errno to
190 0, then call sysconf(), and, if it returns -1, check to see if errno is
191 non-zero.
192 If the value of sysconf(_SC_2_VERSION) is not equal to the value of the
194 _POSIX2_VERSION symbolic constant, the utilities available via system()
195 or popen() might not behave as described in the Shell and Utilities
196 volume of IEEE Std 1003.1-2001. This would mean that the application
197 is not running in an environment that conforms to the Shell and Utili‐
198 ties volume of IEEE Std 1003.1-2001. Some applications might be able to
199 deal with this, others might not. However, the functions defined in
200 this volume of IEEE Std 1003.1-2001 continue to operate as specified,
201 even if sysconf(_SC_2_VERSION) reports that the utilities no longer
202 perform as specified.
203
205 This functionality was added in response to requirements of application
206 developers and of system vendors who deal with many international sys‐
207 tem configurations. It is closely related to pathconf() and fpath‐
208 conf().
209 Although a conforming application can run on all systems by never
211 demanding more resources than the minimum values published in this vol‐
212 ume of IEEE Std 1003.1-2001, it is useful for that application to be
213 able to use the actual value for the quantity of a resource available
214 on any given system. To do this, the application makes use of the value
215 of a symbolic constant in <limits.h> or <unistd.h>.
216 However, once compiled, the application must still be able to cope if
218 the amount of resource available is increased. To that end, an applica‐
219 tion may need a means of determining the quantity of a resource, or the
220 presence of an option, at execution time.
221 Two examples are offered:
223 1. Applications may wish to act differently on systems with or without
225 job control. Applications vendors who wish to distribute only a
226 single binary package to all instances of a computer architecture
227 would be forced to assume job control is never available if it were
228 to rely solely on the <unistd.h> value published in this volume of
229 IEEE Std 1003.1-2001.
230 2. International applications vendors occasionally require knowledge
232 of the number of clock ticks per second. Without these facilities,
233 they would be required to either distribute their applications par‐
234 tially in source form or to have 50 Hz and 60 Hz versions for the
235 various countries in which they operate.
236 It is the knowledge that many applications are actually distributed
238 widely in executable form that leads to this facility. If limited to
239 the most restrictive values in the headers, such applications would
240 have to be prepared to accept the most limited environments offered by
241 the smallest microcomputers. Although this is entirely portable, there
242 was a consensus that they should be able to take advantage of the
243 facilities offered by large systems, without the restrictions associ‐
244 ated with source and object distributions.
245 During the discussions of this feature, it was pointed out that it is
247 almost always possible for an application to discern what a value might
248 be at runtime by suitably testing the various functions themselves.
249 And, in any event, it could always be written to adequately deal with
250 error returns from the various functions. In the end, it was felt that
251 this imposed an unreasonable level of complication and sophistication
252 on the application writer.
253 This runtime facility is not meant to provide ever-changing values that
255 applications have to check multiple times. The values are seen as
256 changing no more frequently than once per system initialization, such
257 as by a system administrator or operator with an automatic configura‐
258 tion program. This volume of IEEE Std 1003.1-2001 specifies that they
259 shall not change within the lifetime of the process.
260 Some values apply to the system overall and others vary at the file
262 system or directory level. The latter are described in pathconf() .
263 Note that all values returned must be expressible as integers. String
265 values were considered, but the additional flexibility of this approach
266 was rejected due to its added complexity of implementation and use.
267 Some values, such as {PATH_MAX}, are sometimes so large that they must
269 not be used to, say, allocate arrays. The sysconf() function returns a
270 negative value to show that this symbolic constant is not even defined
271 in this case.
272 Similar to pathconf(), this permits the implementation not to have a
274 limit. When one resource is infinite, returning an error indicating
275 that some other resource limit has been reached is conforming behavior.
276
278 None.
279
281 confstr(), pathconf(), the Base Definitions volume of
282 IEEE Std 1003.1-2001, <limits.h>, <unistd.h>, the Shell and Utilities
283 volume of IEEE Std 1003.1-2001, getconf
284
286 Portions of this text are reprinted and reproduced in electronic form
287 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
288 -- Portable Operating System Interface (POSIX), The Open Group Base
289 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
290 Electrical and Electronics Engineers, Inc and The Open Group. In the
291 event of any discrepancy between this version and the original IEEE and
292 The Open Group Standard, the original IEEE and The Open Group Standard
293 is the referee document. The original Standard can be obtained online
294 at http://www.opengroup.org/unix/online.html .
295IEEE/The Open Group 2003 SYSCONF(3P)