1SYSCONF(3)                 Linux Programmer's Manual                SYSCONF(3)
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NAME

6       sysconf - Get configuration information at runtime
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SYNOPSIS

9       #include <unistd.h>
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11       long sysconf(int name);
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DESCRIPTION

14       POSIX allows an application to test at compile or run time whether cer‐
15       tain options are supported, or what the value  is  of  certain  config‐
16       urable constants or limits.
17
18       At  compile time this is done by including <unistd.h> and/or <limits.h>
19       and testing the value of certain macros.
20
21       At run time, one can ask for numerical values using the  present  func‐
22       tion  sysconf().   One  can ask for numerical values that may depend on
23       the file system a file is in using the  calls  fpathconf(3)  and  path‐
24       conf(3).  One can ask for string values using confstr(3).
25
26       The  values obtained from these functions are system configuration con‐
27       stants.  They do not change during the lifetime of a process.
28
29       For options, typically, there is a  constant  _POSIX_FOO  that  may  be
30       defined in <unistd.h>.  If it is undefined, one should ask at run time.
31       If it is defined to -1, then the option is not  supported.   If  it  is
32       defined to 0, then relevant functions and headers exist, but one has to
33       ask at runtime what degree of support is available.  If it  is  defined
34       to  a  value other than -1 or 0, then the option is supported.  Usually
35       the value (such as 200112L) indicates the year and month of  the  POSIX
36       revision  describing  the  option.   Glibc uses the value 1 to indicate
37       support as long as the POSIX revision has not been published yet.   The
38       sysconf()  argument  will  be  _SC_FOO.   For  a  list  of options, see
39       posixoptions(7).
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41       For variables or limits, typically, there is  a  constant  _FOO,  maybe
42       defined in <limits.h>, or _POSIX_FOO, maybe defined in <unistd.h>.  The
43       constant will not be defined if the limit is unspecified.  If the  con‐
44       stant  is  defined,  it  gives  a guaranteed value, and a greater value
45       might actually be supported.  If an application wants to take advantage
46       of  values which may change between systems, a call to sysconf() can be
47       made.  The sysconf() argument will be _SC_FOO.
48
49   POSIX.1 Variables
50       We give the name of the variable, the name of  the  sysconf()  argument
51       used to inquire about its value, and a short description.
52
53       First, the POSIX.1 compatible values.
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55       ARG_MAX - _SC_ARG_MAX
56              The  maximum  length  of  the arguments to the exec(3) family of
57              functions.  Must not be less than _POSIX_ARG_MAX (4096).
58
59       CHILD_MAX - _SC_CHILD_MAX
60              The max number of simultaneous processes per user ID.  Must  not
61              be less than _POSIX_CHILD_MAX (25).
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63       HOST_NAME_MAX - _SC_HOST_NAME_MAX
64              Max  length  of  a  hostname, not including the terminating null
65              byte, as returned by gethostname(2).   Must  not  be  less  than
66              _POSIX_HOST_NAME_MAX (255).
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68       LOGIN_NAME_MAX - _SC_LOGIN_NAME_MAX
69              Maximum  length  of a login name, including the terminating null
70              byte.  Must not be less than _POSIX_LOGIN_NAME_MAX (9).
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72       clock ticks - _SC_CLK_TCK
73              The number of clock ticks per second.  The  corresponding  vari‐
74              able  is obsolete.  It was of course called CLK_TCK.  (Note: the
75              macro CLOCKS_PER_SEC does not give information:  it  must  equal
76              1000000.)
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78       OPEN_MAX - _SC_OPEN_MAX
79              The  maximum number of files that a process can have open at any
80              time.  Must not be less than _POSIX_OPEN_MAX (20).
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82       PAGESIZE - _SC_PAGESIZE
83              Size of a page in bytes.  Must not be less than 1.   (Some  sys‐
84              tems use PAGE_SIZE instead.)
85
86       RE_DUP_MAX - _SC_RE_DUP_MAX
87              The  number  of  repeated  occurrences  of  a  BRE  permitted by
88              regexec(3)   and   regcomp(3).    Must   not   be   less    than
89              _POSIX2_RE_DUP_MAX (255).
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91       STREAM_MAX - _SC_STREAM_MAX
92              The  maximum  number  of streams that a process can have open at
93              any time.  If defined, it has the same value as the  standard  C
94              macro FOPEN_MAX.  Must not be less than _POSIX_STREAM_MAX (8).
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96       SYMLOOP_MAX
97              The  maximum  number of symbolic links seen in a pathname before
98              resolution returns ELOOP.  Must not  be  less  than  _POSIX_SYM‐
99              LOOP_MAX (8).
100
101       TTY_NAME_MAX - _SC_TTY_NAME_MAX
102              The maximum length of terminal device name, including the termi‐
103              nating null byte.  Must not  be  less  than  _POSIX_TTY_NAME_MAX
104              (9).
105
106       TZNAME_MAX - _SC_TZNAME_MAX
107              The  maximum  number  of  bytes in a timezone name.  Must not be
108              less than _POSIX_TZNAME_MAX (6).
109
110       _POSIX_VERSION - _SC_VERSION
111              indicates the year and month the POSIX.1 standard  was  approved
112              in  the  format  YYYYMML;  the value 199009L indicates the Sept.
113              1990 revision.
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115   POSIX.2 Variables
116       Next, the POSIX.2 values, giving limits for utilities.
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118       BC_BASE_MAX - _SC_BC_BASE_MAX
119              indicates the maximum obase value accepted by the bc(1) utility.
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121       BC_DIM_MAX - _SC_BC_DIM_MAX
122              indicates the maximum value of elements permitted in an array by
123              bc(1).
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125       BC_SCALE_MAX - _SC_BC_SCALE_MAX
126              indicates the maximum scale value allowed by bc(1).
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128       BC_STRING_MAX - _SC_BC_STRING_MAX
129              indicates the maximum length of a string accepted by bc(1).
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131       COLL_WEIGHTS_MAX - _SC_COLL_WEIGHTS_MAX
132              indicates the maximum numbers of weights that can be assigned to
133              an entry of the LC_COLLATE order keyword in the  locale  defini‐
134              tion file,
135
136       EXPR_NEST_MAX - _SC_EXPR_NEST_MAX
137              is  the maximum number of expressions which can be nested within
138              parentheses by expr(1).
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140       LINE_MAX - _SC_LINE_MAX
141              The maximum length of a utility's input line length, either from
142              standard  input  or  from  a  file.   This includes length for a
143              trailing newline.
144
145       RE_DUP_MAX - _SC_RE_DUP_MAX
146              The maximum number of repeated occurrences of a regular  expres‐
147              sion when the interval notation \{m,n\} is used.
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149       POSIX2_VERSION - _SC_2_VERSION
150              indicates  the  version of the POSIX.2 standard in the format of
151              YYYYMML.
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153       POSIX2_C_DEV - _SC_2_C_DEV
154              indicates whether the POSIX.2 C language development  facilities
155              are supported.
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157       POSIX2_FORT_DEV - _SC_2_FORT_DEV
158              indicates  whether the POSIX.2 FORTRAN development utilities are
159              supported.
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161       POSIX2_FORT_RUN - _SC_2_FORT_RUN
162              indicates whether the POSIX.2 FORTRAN runtime utilities are sup‐
163              ported.
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165       _POSIX2_LOCALEDEF - _SC_2_LOCALEDEF
166              indicates   whether   the   POSIX.2   creation  of  locates  via
167              localedef(1) is supported.
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169       POSIX2_SW_DEV - _SC_2_SW_DEV
170              indicates whether the  POSIX.2  software  development  utilities
171              option is supported.
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173       These values also exist, but may not be standard.
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175        - _SC_PHYS_PAGES
176              The  number of pages of physical memory.  Note that it is possi‐
177              ble for the product of this value and the value of _SC_PAGE_SIZE
178              to overflow.
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180        - _SC_AVPHYS_PAGES
181              The number of currently available pages of physical memory.
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183        - _SC_NPROCESSORS_CONF
184              The number of processors configured.
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186        - _SC_NPROCESSORS_ONLN
187              The number of processors currently online (available).
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RETURN VALUE

190       If name is invalid, -1 is returned, and errno is set to EINVAL.  Other‐
191       wise, the value returned is the value of the system resource and  errno
192       is  not  changed.  In the case of options, a positive value is returned
193       if a queried option is available, and -1 if it is not.  In the case  of
194       limits, -1 means that there is no definite limit.
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CONFORMING TO

197       POSIX.1-2001.
198

BUGS

200       It  is difficult to use ARG_MAX because it is not specified how much of
201       the argument space for exec(3) is consumed by  the  user's  environment
202       variables.
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204       Some  returned values may be huge; they are not suitable for allocating
205       memory.
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SEE ALSO

208       bc(1),  expr(1),  getconf(1),  locale(1),  fpathconf(3),   pathconf(3),
209       posixoptions(7)
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COLOPHON

212       This  page  is  part of release 3.25 of the Linux man-pages project.  A
213       description of the project, and information about reporting  bugs,  can
214       be found at http://www.kernel.org/doc/man-pages/.
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218GNU                               2007-12-12                        SYSCONF(3)
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