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30 .\" @(#)sysconf.3 8.3 (Berkeley) 4/19/94
31 .\"
32 .Dd August 6, 2008
33 .Dt SYSCONF 3
34 .Os
35 .Sh NAME
36 .Nm sysconf
37 .Nd get configurable system variables
38 .Sh LIBRARY
39 .Lb libc
40 .Sh SYNOPSIS
41 .In unistd.h
42 .Ft long
43 .Fn sysconf "int name"
44 .Sh DESCRIPTION
45 This interface is defined by
46 .St -p1003.1-88 .
47 A far more complete interface is available using
48 .Xr sysctl 3 .
49 .Pp
50 The
51 .Fn sysconf
52 function provides a method for applications to determine the current
53 value of a configurable system limit or option variable.
54 The
55 .Fa name
56 argument specifies the system variable to be queried.
57 Symbolic constants for each name value are found in the include file
58 .In unistd.h .
59 .Pp
60 The available values are as follows:
61 .Bl -tag -width "123456"
62 .It Li _SC_ARG_MAX
63 The maximum bytes of argument to
64 .Xr execve 2 .
65 .It Li _SC_ATEXIT_MAX
66 The maxmimum number of functions that may be registered with
67 .Xr atexit 3 .
68 .It Li _SC_BARRIERS
69 The version of
70 .St -p1003.1
71 and its
72 Barriers
73 option to which the system attempts to conform,
74 otherwise \-1.
75 .It Li _SC_CLOCK_SELECTION
76 Return the
77 .Tn POSIX
78 version the implementation of the Clock Selection Option
79 on this system conforms to,
80 or \-1 if unavailable.
81 .It Li _SC_CHILD_MAX
82 The maximum number of simultaneous processes per user id.
83 .It Li _SC_CLK_TCK
84 The number of clock ticks per second.
85 .It Li _SC_FSYNC
86 Return 1 if the File Synchronization Option is available on this system,
87 otherwise \-1.
88 .It Li _SC_HOST_NAME_MAX
89 The maximum size of a hostname, including NULL.
90 .It Li _SC_IOV_MAX
91 The maximum number of
92 .Va iovec
93 structures that a process has available for use with
94 .Xr preadv 2 ,
95 .Xr pwritev 2 ,
96 .Xr readv 2 ,
97 .Xr recvmsg 2 ,
98 .Xr sendmsg 2
99 or
100 .Xr writev 2 .
101 .It Li _SC_JOB_CONTROL
102 Return 1 if job control is available on this system, otherwise \-1.
103 .It Li _SC_LOGIN_NAME_MAX
104 Returns the size of the storage required for a login name, in bytes,
105 including the terminating NUL.
106 .It Li _SC_MAPPED_FILES
107 Return 1 if the Memory Mapped Files Option is available on this system,
108 otherwise \-1.
109 .It Li _SC_MEMLOCK
110 Return 1 if the Process Memory Locking Option is available on this system,
111 otherwise \-1.
112 .It Li _SC_MEMLOCK_RANGE
113 Return 1 if the Range Memory Locking Option is available on this system,
114 otherwise \-1.
115 .It Li _SC_MEMORY_PROTECTION
116 Return 1 if the Memory Protection Option is available on this system,
117 otherwise \-1.
118 .It Li _SC_MONOTONIC_CLOCK
119 Return the
120 .Tn POSIX
121 version the implementation of the Monotonic Clock Option
122 on this system conforms to,
123 or \-1 if unavailable.
124 .It Li _SC_NGROUPS_MAX
125 The maximum number of supplemental groups.
126 .It Li _SC_OPEN_MAX
127 The maximum number of open files per process.
128 .It Li _SC_PAGESIZE
129 The size of a system page in bytes.
130 .It Li _SC_PASS_MAX
131 The maximum length of the password, not counting NULL.
132 .It Li _SC_READER_WRITER_LOCKS
133 The version of
134 .St -p1003.1
135 and its
136 Read-Write Locks
137 option to which the system attempts to conform,
138 otherwise \-1.
139 .It Li _SC_REGEXP
140 Return 1 if
141 .Tn POSIX
142 regular expressions are available on this system, otherwise \-1.
143 .It Li _SC_SEMAPHORES
144 The version of
145 .St -p1003.1
146 and its
147 Semaphores
148 option to which the system attempts to conform,
149 otherwise \-1.
150 .Pp
151 Availability of the
152 Semaphores
153 option depends on the
154 .Li P1003_1B_SEMAPHORE
155 kernel option.
156 .It Li _SC_SHELL
157 Return 1 if
158 .Tn POSIX
159 shell is available on this system, otherwise \-1.
160 .It Li _SC_SPIN_LOCKS
161 The version of
162 .St -p1003.1
163 and its
164 Spin Locks
165 option to which the system attempts to conform,
166 otherwise \-1.
167 .It Li _SC_STREAM_MAX
168 The minimum maximum number of streams that a process may have open
169 at any one time.
170 .It Li _SC_SYMLOOP_MAX
171 The maximum number of symbolic links that may be expanded in a path name.
172 .It Li _SC_SYNCHRONIZED_IO
173 Return 1 if the Synchronized I/O Option is available on this system,
174 otherwise \-1.
175 .It Li _SC_THREADS
176 The version of
177 .St -p1003.1
178 and its
179 Threads
180 option to which the system attempts to conform,
181 otherwise \-1.
182 .It Li _SC_TIMERS
183 The version of
184 .St -p1003.1
185 and its
186 Timers
187 option to which the system attempts to conform,
188 otherwise \-1.
189 .It Li _SC_TZNAME_MAX
190 The minimum maximum number of types supported for the name of a
191 timezone.
192 .It Li _SC_SAVED_IDS
193 Returns 1 if saved set-group and saved set-user ID is available,
194 otherwise \-1.
195 .It Li _SC_VERSION
196 The version of ISO/IEC 9945 (POSIX 1003.1) with which the system
197 attempts to comply.
198 .It Li _SC_XOPEN_SHM
199 Return 1 if the
200 .St -xpg4.2
201 Shared Memory
202 option is available on this system,
203 otherwise \-1.
204 .Pp
205 Availability of the
206 Shared Memory
207 option depends on the
208 .Li SYSVSHM
209 kernel option.
210 .It Li _SC_BC_BASE_MAX
211 The maximum ibase/obase values in the
212 .Xr bc 1
213 utility.
214 .It Li _SC_BC_DIM_MAX
215 The maximum array size in the
216 .Xr bc 1
217 utility.
218 .It Li _SC_BC_SCALE_MAX
219 The maximum scale value in the
220 .Xr bc 1
221 utility.
222 .It Li _SC_BC_STRING_MAX
223 The maximum string length in the
224 .Xr bc 1
225 utility.
226 .It Li _SC_COLL_WEIGHTS_MAX
227 The maximum number of weights that can be assigned to any entry of
228 the LC_COLLATE order keyword in the locale definition file.
229 .It Li _SC_EXPR_NEST_MAX
230 The maximum number of expressions that can be nested within
231 parenthesis by the
232 .Xr expr 1
233 utility.
234 .It Li _SC_LINE_MAX
235 The maximum length in bytes of a text-processing utility's input
236 line.
237 .It Li _SC_RE_DUP_MAX
238 The maximum number of repeated occurrences of a regular expression
239 permitted when using interval notation.
240 .It Li _SC_2_VERSION
241 The version of POSIX 1003.2 with which the system attempts to comply.
242 .It Li _SC_2_C_BIND
243 Return 1 if the system's C-language development facilities support the
244 C-Language Bindings Option, otherwise \-1.
245 .It Li _SC_2_C_DEV
246 Return 1 if the system supports the C-Language Development Utilities Option,
247 otherwise \-1.
248 .It Li _SC_2_CHAR_TERM
249 Return 1 if the system supports at least one terminal type capable of
250 all operations described in POSIX 1003.2, otherwise \-1.
251 .It Li _SC_2_FORT_DEV
252 Return 1 if the system supports the FORTRAN Development Utilities Option,
253 otherwise \-1.
254 .It Li _SC_2_FORT_RUN
255 Return 1 if the system supports the FORTRAN Runtime Utilities Option,
256 otherwise \-1.
257 .It Li _SC_2_LOCALEDEF
258 Return 1 if the system supports the creation of locales, otherwise \-1.
259 .It Li _SC_2_SW_DEV
260 Return 1 if the system supports the Software Development Utilities Option,
261 otherwise \-1.
262 .It Li _SC_2_UPE
263 Return 1 if the system supports the User Portability Utilities Option,
264 otherwise \-1.
265 .It Li _SC_GETGR_R_SIZE_MAX
266 The minimum size of the
267 .Fa buffer
268 passed to
269 .Xr getgrgid_r 3
270 and
271 .Xr getgrnam_r 3 .
272 .It Li _SC_GETPW_R_SIZE_MAX
273 The minimum size of the
274 .Fa buffer
275 passed to
276 .Xr getpwnam_r 3
277 and
278 .Xr getpwuid_r 3 .
279 .It Li _SC_NPROCESSORS_CONF
280 The number of processors configured.
281 .It Li _SC_NPROCESSORS_ONLN
282 The number of processors online (capable of running processes).
283 .El
284 .Sh RETURN VALUES
285 If the call to
286 .Nm sysconf
287 is not successful, \-1 is returned and
288 .Va errno
289 is set appropriately.
290 Otherwise, if the variable is associated with functionality that is not
291 supported, \-1 is returned and
292 .Va errno
293 is not modified.
294 Otherwise, the current variable value is returned.
295 .Sh ERRORS
296 The
297 .Fn sysconf
298 function may fail and set
299 .Va errno
300 for any of the errors specified for the library functions
301 .Xr sysctl 3 .
302 In addition, the following error may be reported:
303 .Bl -tag -width Er
304 .It Bq Er EINVAL
305 The value of the
306 .Fa name
307 argument is invalid.
308 .El
309 .Sh SEE ALSO
310 .Xr sysctl 3
311 .Sh STANDARDS
312 The
313 .Fn sysconf
314 function conforms to
315 .St -p1003.1-90 .
316 The constants
317 .Li _SC_NPROCESSORS_CONF
318 and
319 .Li _SC_NPROCESSORS_ONLN
320 are not part of the standard, but are provided by many systems.
321 .Sh HISTORY
322 The
323 .Nm sysconf
324 function first appeared in
325 .Bx 4.4 .
326 .Sh BUGS
327 The value for _SC_STREAM_MAX is a minimum maximum, and required to be
328 the same as ANSI C's FOPEN_MAX, so the returned value is a ridiculously
329 small and misleading number.