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SYSCONF(3P)                POSIX Programmer's Manual               SYSCONF(3P)
PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the  corresponding
       Linux  manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.
NAME
       sysconf -- get configurable system variables
SYNOPSIS
       #include <unistd.h>
       long sysconf(int name);
DESCRIPTION
       The sysconf() function provides a method for the application to  deter-
       mine  the current value of a configurable system limit or option (vari-
       able).  The implementation shall support all of the variables listed in
       the following table and may support others.
       The  name  argument  represents  the system variable to be queried. The
       following table lists the minimal set of system  variables  from  <lim-
       its.h>  or  <unistd.h>  that can be returned by sysconf(), and the sym-
       bolic constants defined in <unistd.h> that are the corresponding values
       used for name.
        +---------------------------------+----------------------------------+
        |            Variable             |          Value of Name           |
        +---------------------------------+----------------------------------+
        |{AIO_LISTIO_MAX}                 |_SC_AIO_LISTIO_MAX                |
        |{AIO_MAX}                        |_SC_AIO_MAX                       |
        |{AIO_PRIO_DELTA_MAX}             |_SC_AIO_PRIO_DELTA_MAX            |
        |{ARG_MAX}                        |_SC_ARG_MAX                       |
        |{ATEXIT_MAX}                     |_SC_ATEXIT_MAX                    |
        |{BC_BASE_MAX}                    |_SC_BC_BASE_MAX                   |
        |{BC_DIM_MAX}                     |_SC_BC_DIM_MAX                    |
        |{BC_SCALE_MAX}                   |_SC_BC_SCALE_MAX                  |
        |{BC_STRING_MAX}                  |_SC_BC_STRING_MAX                 |
        |{CHILD_MAX}                      |_SC_CHILD_MAX                     |
        |Clock ticks/second               |_SC_CLK_TCK                       |
        |{COLL_WEIGHTS_MAX}               |_SC_COLL_WEIGHTS_MAX              |
        |{DELAYTIMER_MAX}                 |_SC_DELAYTIMER_MAX                |
        |{EXPR_NEST_MAX}                  |_SC_EXPR_NEST_MAX                 |
        |{HOST_NAME_MAX}                  |_SC_HOST_NAME_MAX                 |
        |{IOV_MAX}                        |_SC_IOV_MAX                       |
        |{LINE_MAX}                       |_SC_LINE_MAX                      |
        |{LOGIN_NAME_MAX}                 |_SC_LOGIN_NAME_MAX                |
        |{NGROUPS_MAX}                    |_SC_NGROUPS_MAX                   |
        |Initial size of getgrgid_r() and |_SC_GETGR_R_SIZE_MAX              |
        |getgrnam_r() data buffers        |                                  |
        |Initial size of getpwuid_r() and |_SC_GETPW_R_SIZE_MAX              |
        |getpwnam_r() data buffers        |                                  |
        |{MQ_OPEN_MAX}                    |_SC_MQ_OPEN_MAX                   |
        |{MQ_PRIO_MAX}                    |_SC_MQ_PRIO_MAX                   |
        |{OPEN_MAX}                       |_SC_OPEN_MAX                      |
        |_POSIX_ADVISORY_INFO             |_SC_ADVISORY_INFO                 |
        |_POSIX_BARRIERS                  |_SC_BARRIERS                      |
        |_POSIX_ASYNCHRONOUS_IO           |_SC_ASYNCHRONOUS_IO               |
        |_POSIX_CLOCK_SELECTION           |_SC_CLOCK_SELECTION               |
        |_POSIX_CPUTIME                   |_SC_CPUTIME                       |
        |_POSIX_FSYNC                     |_SC_FSYNC                         |
        |_POSIX_IPV6                      |_SC_IPV6                          |
        |_POSIX_JOB_CONTROL               |_SC_JOB_CONTROL                   |
        |_POSIX_MAPPED_FILES              |_SC_MAPPED_FILES                  |
        |_POSIX_MEMLOCK                   |_SC_MEMLOCK                       |
        |_POSIX_MEMLOCK_RANGE             |_SC_MEMLOCK_RANGE                 |
        |_POSIX_MEMORY_PROTECTION         |_SC_MEMORY_PROTECTION             |
        |_POSIX_MESSAGE_PASSING           |_SC_MESSAGE_PASSING               |
        |_POSIX_MONOTONIC_CLOCK           |_SC_MONOTONIC_CLOCK               |
        |_POSIX_PRIORITIZED_IO            |_SC_PRIORITIZED_IO                |
        |_POSIX_PRIORITY_SCHEDULING       |_SC_PRIORITY_SCHEDULING           |
        |_POSIX_RAW_SOCKETS               |_SC_RAW_SOCKETS                   |
        |_POSIX_READER_WRITER_LOCKS       |_SC_READER_WRITER_LOCKS           |
        |_POSIX_REALTIME_SIGNALS          |_SC_REALTIME_SIGNALS              |
        |_POSIX_REGEXP                    |_SC_REGEXP                        |
        |_POSIX_SAVED_IDS                 |_SC_SAVED_IDS                     |
        |_POSIX_SEMAPHORES                |_SC_SEMAPHORES                    |
        |_POSIX_SHARED_MEMORY_OBJECTS     |_SC_SHARED_MEMORY_OBJECTS         |
        |_POSIX_SHELL                     |_SC_SHELL                         |
        |_POSIX_SPAWN                     |_SC_SPAWN                         |
        |_POSIX_SPIN_LOCKS                |_SC_SPIN_LOCKS                    |
        |_POSIX_SPORADIC_SERVER           |_SC_SPORADIC_SERVER               |
        |_POSIX_SS_REPL_MAX               |_SC_SS_REPL_MAX                   |
        |_POSIX_SYNCHRONIZED_IO           |_SC_SYNCHRONIZED_IO               |
        |_POSIX_THREAD_ATTR_STACKADDR     |_SC_THREAD_ATTR_STACKADDR         |
        |_POSIX_THREAD_ATTR_STACKSIZE     |_SC_THREAD_ATTR_STACKSIZE         |
        |_POSIX_THREAD_CPUTIME            |_SC_THREAD_CPUTIME                |
        |_POSIX_THREAD_PRIO_INHERIT       |_SC_THREAD_PRIO_INHERIT           |
        |_POSIX_THREAD_PRIO_PROTECT       |_SC_THREAD_PRIO_PROTECT           |
        |_POSIX_THREAD_PRIORITY_SCHEDULING|_SC_THREAD_PRIORITY_SCHEDULING    |
        |_POSIX_THREAD_PROCESS_SHARED     |_SC_THREAD_PROCESS_SHARED         |
        |_POSIX_THREAD_ROBUST_PRIO_INHERIT|_SC_THREAD_ROBUST_PRIO_INHERIT    |
        |_POSIX_THREAD_ROBUST_PRIO_PROTECT|_SC_THREAD_ROBUST_PRIO_PROTECT    |
        |_POSIX_THREAD_SAFE_FUNCTIONS     |_SC_THREAD_SAFE_FUNCTIONS         |
        |_POSIX_THREAD_SPORADIC_SERVER    |_SC_THREAD_SPORADIC_SERVER        |
        |_POSIX_THREADS                   |_SC_THREADS                       |
        |_POSIX_TIMEOUTS                  |_SC_TIMEOUTS                      |
        |_POSIX_TIMERS                    |_SC_TIMERS                        |
        |_POSIX_TRACE                     |_SC_TRACE                         |
        |_POSIX_TRACE_EVENT_FILTER        |_SC_TRACE_EVENT_FILTER            |
        |_POSIX_TRACE_EVENT_NAME_MAX      |_SC_TRACE_EVENT_NAME_MAX          |
        |_POSIX_TRACE_INHERIT             |_SC_TRACE_INHERIT                 |
        |_POSIX_TRACE_LOG                 |_SC_TRACE_LOG                     |
        |_POSIX_TRACE_NAME_MAX            |_SC_TRACE_NAME_MAX                |
        |_POSIX_TRACE_SYS_MAX             |_SC_TRACE_SYS_MAX                 |
        |_POSIX_TRACE_USER_EVENT_MAX      |_SC_TRACE_USER_EVENT_MAX          |
        |_POSIX_TYPED_MEMORY_OBJECTS      |_SC_TYPED_MEMORY_OBJECTS          |
        |_POSIX_VERSION                   |_SC_VERSION                       |
        |_POSIX_V7_ILP32_OFF32            |_SC_V7_ILP32_OFF32                |
        |_POSIX_V7_ILP32_OFFBIG           |_SC_V7_ILP32_OFFBIG               |
        |_POSIX_V7_LP64_OFF64             |_SC_V7_LP64_OFF64                 |
        |_POSIX_V7_LPBIG_OFFBIG           |_SC_V7_LPBIG_OFFBIG               |
        +---------------------------------+----------------------------------+
         +--------------------------------+---------------------------------+
         |            Variable            |         Value of Name           |
         +--------------------------------+---------------------------------+
         |_POSIX_V6_ILP32_OFF32           |_SC_V6_ILP32_OFF32               |
         |_POSIX_V6_ILP32_OFFBIG          |_SC_V6_ILP32_OFFBIG              |
         |_POSIX_V6_LP64_OFF64            |_SC_V6_LP64_OFF64                |
         |_POSIX_V6_LPBIG_OFFBIG          |_SC_V6_LPBIG_OFFBIG              |
         |_POSIX2_C_BIND                  |_SC_2_C_BIND                     |
         |_POSIX2_C_DEV                   |_SC_2_C_DEV                      |
         |_POSIX2_CHAR_TERM               |_SC_2_CHAR_TERM                  |
         |_POSIX2_FORT_DEV                |_SC_2_FORT_DEV                   |
         |_POSIX2_FORT_RUN                |_SC_2_FORT_RUN                   |
         |_POSIX2_LOCALEDEF               |_SC_2_LOCALEDEF                  |
         |_POSIX2_PBS                     |_SC_2_PBS                        |
         |_POSIX2_PBS_ACCOUNTING          |_SC_2_PBS_ACCOUNTING             |
         |_POSIX2_PBS_CHECKPOINT          |_SC_2_PBS_CHECKPOINT             |
         |_POSIX2_PBS_LOCATE              |_SC_2_PBS_LOCATE                 |
         |_POSIX2_PBS_MESSAGE             |_SC_2_PBS_MESSAGE                |
         |_POSIX2_PBS_TRACK               |_SC_2_PBS_TRACK                  |
         |_POSIX2_SW_DEV                  |_SC_2_SW_DEV                     |
         |_POSIX2_UPE                     |_SC_2_UPE                        |
         |_POSIX2_VERSION                 |_SC_2_VERSION                    |
         |{PAGE_SIZE}                     |_SC_PAGE_SIZE                    |
         |{PAGESIZE}                      |_SC_PAGESIZE                     |
         |{PTHREAD_DESTRUCTOR_ITERATIONS} |_SC_THREAD_DESTRUCTOR_ITERATIONS |
         |{PTHREAD_KEYS_MAX}              |_SC_THREAD_KEYS_MAX              |
         |{PTHREAD_STACK_MIN}             |_SC_THREAD_STACK_MIN             |
         |{PTHREAD_THREADS_MAX}           |_SC_THREAD_THREADS_MAX           |
         |{RE_DUP_MAX}                    |_SC_RE_DUP_MAX                   |
         |{RTSIG_MAX}                     |_SC_RTSIG_MAX                    |
         |{SEM_NSEMS_MAX}                 |_SC_SEM_NSEMS_MAX                |
         |{SEM_VALUE_MAX}                 |_SC_SEM_VALUE_MAX                |
         |{SIGQUEUE_MAX}                  |_SC_SIGQUEUE_MAX                 |
         |{STREAM_MAX}                    |_SC_STREAM_MAX                   |
         |{SYMLOOP_MAX}                   |_SC_SYMLOOP_MAX                  |
         |{TIMER_MAX}                     |_SC_TIMER_MAX                    |
         |{TTY_NAME_MAX}                  |_SC_TTY_NAME_MAX                 |
         |{TZNAME_MAX}                    |_SC_TZNAME_MAX                   |
         |_XOPEN_CRYPT                    |_SC_XOPEN_CRYPT                  |
         |_XOPEN_ENH_I18N                 |_SC_XOPEN_ENH_I18N               |
         |_XOPEN_REALTIME                 |_SC_XOPEN_REALTIME               |
         |_XOPEN_REALTIME_THREADS         |_SC_XOPEN_REALTIME_THREADS       |
         |_XOPEN_SHM                      |_SC_XOPEN_SHM                    |
         |_XOPEN_STREAMS                  |_SC_XOPEN_STREAMS                |
         |_XOPEN_UNIX                     |_SC_XOPEN_UNIX                   |
         |_XOPEN_UUCP                     |_SC_XOPEN_UUCP                   |
         |_XOPEN_VERSION                  |_SC_XOPEN_VERSION                |
         +--------------------------------+---------------------------------+
RETURN VALUE
       If name is an invalid value, sysconf() shall return -1 and set errno to
       indicate the error. If the variable corresponding to name is  described
       in  <limits.h>  as  a  maximum or minimum value and the variable has no
       limit, sysconf() shall return -1 without changing the value  of  errno.
       Note  that  indefinite  limits  do not imply infinite limits; see <lim-
       its.h>.
       Otherwise, sysconf() shall return the current  variable  value  on  the
       system.  The value returned shall not be more restrictive than the cor-
       responding value described to the application when it was compiled with
       the  implementation's  <limits.h>  or  <unistd.h>.  The value shall not
       change  during  the  lifetime  of  the  calling  process,  except  that
       sysconf(_SC_OPEN_MAX)  may  return  different values before and after a
       call to setrlimit() which changes the RLIMIT_NOFILE soft limit.
       If the variable corresponding to name is dependent  on  an  unsupported
       option, the results are unspecified.
ERRORS
       The sysconf() function shall fail if:
       EINVAL The value of the name argument is invalid.
       The following sections are informative.
EXAMPLES
       None.
APPLICATION USAGE
       As  -1  is  a  permissible  return  value in a successful situation, an
       application wishing to check for error situations should set  errno  to
       0, then call sysconf(), and, if it returns -1, check to see if errno is
       non-zero.
       Application  developers  should  check  whether  an  option,  such   as
       _POSIX_TRACE,  is  supported  prior  to  obtaining and using values for
       related variables, such as _POSIX_TRACE_NAME_MAX.
RATIONALE
       This functionality was added in response to requirements of application
       developers  and of system vendors who deal with many international sys-
       tem configurations. It is closely  related  to  pathconf()  and  fpath-
       conf().
       Although  a  conforming  application  can  run  on all systems by never
       demanding more resources than the minimum values published in this vol-
       ume  of  POSIX.1-2008,  it is useful for that application to be able to
       use the actual value for the quantity of a resource  available  on  any
       given  system.  To do this, the application makes use of the value of a
       symbolic constant in <limits.h> or <unistd.h>.
       However, once compiled, the application must still be able to  cope  if
       the amount of resource available is increased. To that end, an applica-
       tion may need a means of determining the quantity of a resource, or the
       presence of an option, at execution time.
       Two examples are offered:
        1. Applications may wish to act differently on systems with or without
           job control.  Applications vendors who wish to  distribute  only  a
           single  binary  package to all instances of a computer architecture
           would be forced to assume job control is never available if it were
           to  rely solely on the <unistd.h> value published in this volume of
           POSIX.1-2008.
        2. International applications vendors occasionally  require  knowledge
           of the number of clock ticks per second.  Without these facilities,
           they would be required to either distribute their applications par-
           tially  in  source form or to have 50 Hz and 60 Hz versions for the
           various countries in which they operate.
       It is the knowledge that many  applications  are  actually  distributed
       widely  in  executable  form that leads to this facility. If limited to
       the most restrictive values in the  headers,  such  applications  would
       have  to be prepared to accept the most limited environments offered by
       the smallest microcomputers. Although this is entirely portable,  there
       was  a  consensus  that  they  should  be able to take advantage of the
       facilities offered by large systems, without the  restrictions  associ-
       ated with source and object distributions.
       During  the  discussions of this feature, it was pointed out that it is
       almost always possible for an application to discern what a value might
       be  at  runtime  by  suitably testing the various functions themselves.
       And, in any event, it could always be written to adequately  deal  with
       error  returns from the various functions. In the end, it was felt that
       this imposed an unreasonable level of complication  and  sophistication
       on the application developer.
       This runtime facility is not meant to provide ever-changing values that
       applications have to check multiple  times.  The  values  are  seen  as
       changing  no  more frequently than once per system initialization, such
       as by a system administrator or operator with an  automatic  configura-
       tion program. This volume of POSIX.1-2008 specifies that they shall not
       change within the lifetime of the process.
       Some values apply to the system overall and others  vary  at  the  file
       system or directory level. The latter are described in fpathconf().
       Note  that  all values returned must be expressible as integers. String
       values were considered, but the additional flexibility of this approach
       was rejected due to its added complexity of implementation and use.
       Some  values, such as {PATH_MAX}, are sometimes so large that they must
       not be used to, say, allocate arrays. The sysconf() function returns  a
       negative  value to show that this symbolic constant is not even defined
       in this case.
       Similar to pathconf(), this permits the implementation not  to  have  a
       limit.  When  one  resource  is infinite, returning an error indicating
       that some other resource limit has been reached is conforming behavior.
FUTURE DIRECTIONS
       None.
SEE ALSO
       confstr(), fpathconf()
       The Base Definitions volume of POSIX.1-2008, <limits.h>, <unistd.h>
       The Shell and Utilities volume of POSIX.1-2008, getconf
COPYRIGHT
       Portions of this text are reprinted and reproduced in  electronic  form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX),  The  Open  Group  Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri-
       cal and Electronics Engineers,  Inc  and  The  Open  Group.   (This  is
       POSIX.1-2008  with  the  2013  Technical Corrigendum 1 applied.) In the
       event of any discrepancy between this version and the original IEEE and
       The  Open Group Standard, the original IEEE and The Open Group Standard
       is the referee document. The original Standard can be  obtained  online
       at http://www.unix.org/online.html .
       Any  typographical  or  formatting  errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files  to  man page format. To report such errors, see https://www.ker-
       nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group                  2013                          SYSCONF(3P)