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#### 31.4.2 Constants for `sysconf` Parameters

Here are the symbolic constants for use as the parameter argument to `sysconf`. The values are all integer constants (more specifically, enumeration type values).

`_SC_ARG_MAX`
  Inquire about the parameter corresponding to `ARG_MAX`.
`_SC_CHILD_MAX`
  Inquire about the parameter corresponding to `CHILD_MAX`.
`_SC_OPEN_MAX`
  Inquire about the parameter corresponding to `OPEN_MAX`.
`_SC_STREAM_MAX`
  Inquire about the parameter corresponding to `STREAM_MAX`.
`_SC_TZNAME_MAX`
  Inquire about the parameter corresponding to `TZNAME_MAX`.
`_SC_NGROUPS_MAX`
  Inquire about the parameter corresponding to `NGROUPS_MAX`.
`_SC_JOB_CONTROL`
  Inquire about the parameter corresponding to `_POSIX_JOB_CONTROL`.
`_SC_SAVED_IDS`
  Inquire about the parameter corresponding to `_POSIX_SAVED_IDS`.
`_SC_VERSION`
  Inquire about the parameter corresponding to `_POSIX_VERSION`.
`_SC_CLK_TCK`
  Inquire about the number of clock ticks per second; see CPU Time. The corresponding parameter `CLK_TCK` is obsolete.
`_SC_CHARCLASS_NAME_MAX`
  Inquire about the parameter corresponding to maximal length allowed for a character class name in an extended locale specification. These extensions are not yet standardized and so this option is not standardized as well.
`_SC_REALTIME_SIGNALS`
  Inquire about the parameter corresponding to `_POSIX_REALTIME_SIGNALS`.
`_SC_PRIORITY_SCHEDULING`
  Inquire about the parameter corresponding to `_POSIX_PRIORITY_SCHEDULING`.
`_SC_TIMERS`
  Inquire about the parameter corresponding to `_POSIX_TIMERS`.
`_SC_ASYNCHRONOUS_IO`
  Inquire about the parameter corresponding to `_POSIX_ASYNCHRONOUS_IO`.
`_SC_PRIORITIZED_IO`
  Inquire about the parameter corresponding to `_POSIX_PRIORITIZED_IO`.
`_SC_SYNCHRONIZED_IO`
  Inquire about the parameter corresponding to `_POSIX_SYNCHRONIZED_IO`.
`_SC_FSYNC`
  Inquire about the parameter corresponding to `_POSIX_FSYNC`.
`_SC_MAPPED_FILES`
  Inquire about the parameter corresponding to `_POSIX_MAPPED_FILES`.
`_SC_MEMLOCK`
  Inquire about the parameter corresponding to `_POSIX_MEMLOCK`.
`_SC_MEMLOCK_RANGE`
  Inquire about the parameter corresponding to `_POSIX_MEMLOCK_RANGE`.
`_SC_MEMORY_PROTECTION`
  Inquire about the parameter corresponding to `_POSIX_MEMORY_PROTECTION`.
`_SC_MESSAGE_PASSING`
  Inquire about the parameter corresponding to `_POSIX_MESSAGE_PASSING`.
`_SC_SEMAPHORES`
  Inquire about the parameter corresponding to `_POSIX_SEMAPHORES`.
`_SC_SHARED_MEMORY_OBJECTS`
  Inquire about the parameter corresponding to
  `_POSIX_SHARED_MEMORY_OBJECTS`.
`_SC_AIO_LISTIO_MAX`
  Inquire about the parameter corresponding to `_POSIX_AIO_LISTIO_MAX`.
`_SC_AIO_MAX`
  Inquire about the parameter corresponding to `_POSIX_AIO_MAX`.
`_SC_AIO_PRIO_DELTA_MAX`
  Inquire the value by which a process can decrease its asynchronous I/O priority level from its own scheduling priority. This corresponds to the run-time invariant value `AIO_PRIO_DELTA_MAX`.
`_SC_DELAYTIMER_MAX`
  Inquire about the parameter corresponding to `_POSIX_DELAYTIMER_MAX`.
`_SC_MQ_OPEN_MAX`
  Inquire about the parameter corresponding to `_POSIX_MQ_OPEN_MAX`.
`_SC_MQ_PRIO_MAX`
  Inquire about the parameter corresponding to `_POSIX_MQ_PRIO_MAX`.
`_SC_RTSIG_MAX`
  Inquire about the parameter corresponding to `_POSIX_RTSIG_MAX`.
`_SC_SEM_NSEMS_MAX`
  Inquire about the parameter corresponding to `_POSIX_SEM_NSEMS_MAX`.
`_SC_SEM_VALUE_MAX`
  Inquire about the parameter corresponding to `_POSIX_SEM_VALUE_MAX`.
`_SC_SIGQUEUE_MAX`
  Inquire about the parameter corresponding to `_POSIX_SIGQUEUE_MAX`.
`_SC_TIMER_MAX`
  Inquire about the parameter corresponding to `_POSIX_TIMER_MAX`.
`_SC_PII`
  Inquire about the parameter corresponding to `_POSIX_PII`.
`_SC_PII_XTI`
  Inquire about the parameter corresponding to `_POSIX_PII_XTI`.
`_SC_PII_SOCKET`
  Inquire about the parameter corresponding to `_POSIX_PII_SOCKET`.
`_SC_PII_INTERNET`
  Inquire about the parameter corresponding to `_POSIX_PII_INTERNET`.
`_SC_PII_OSI`
  Inquire about the parameter corresponding to `_POSIX_PII_OSI`.
`_SC_SELECT`
  Inquire about the parameter corresponding to `_POSIX_SELECT`.
`_SC_UIO_MAXIOV`
  Inquire about the parameter corresponding to `_POSIX_UIO_MAXIOV`.
`_SC_PII_INTERNET_STREAM`
  Inquire about the parameter corresponding to `_POSIX_PII_INTERNET_STREAM`.
`_SC_PII_INTERNET_DGRAM`
  Inquire about the parameter corresponding to `_POSIX_PII_INTERNET_DGRAM`.
`_SC_PII_OSI_COTS`
  Inquire about the parameter corresponding to `_POSIX_PII_OSI_COTS`.
`_SC_PII_OSI_CLTS`
  Inquire about the parameter corresponding to `_POSIX_PII_OSI_CLTS`.
`_SC_PII_OSI_M`
  Inquire about the parameter corresponding to `_POSIX_PII_OSI_M`.
`_SC_T_IOV_MAX`
  Inquire the value of the value associated with the `T_IOV_MAX` variable.
`_SC_THREADS`
  Inquire about the parameter corresponding to `_POSIX_THREADS`.
`_SC_THREAD_SAFE_FUNCTIONS`
  Inquire about the parameter corresponding to
  `_POSIX_THREAD_SAFE_FUNCTIONS`.
`_SC_GETGR_R_SIZE_MAX`
  Inquire about the parameter corresponding to `_POSIX_GETGR_R_SIZE_MAX`.
`_SC_GETPW_R_SIZE_MAX`
  Inquire about the parameter corresponding to `_POSIX_GETPW_R_SIZE_MAX`.
`_SC_LOGIN_NAME_MAX`
  Inquire about the parameter corresponding to `_POSIX_LOGIN_NAME_MAX`.
`_SC_TTY_NAME_MAX`
  Inquire about the parameter corresponding to `_POSIX_TTY_NAME_MAX`.
`_SC_THREAD_DESTRUCTOR_ITERATIONS`
  Inquire about the parameter corresponding to `_POSIX_THREAD_DESTRUCTOR_ITERATIONS`.
`_SC_THREAD_KEYS_MAX`
  Inquire about the parameter corresponding to `_POSIX_THREAD_KEYS_MAX`.
`_SC_THREAD_STACK_MIN`
  Inquire about the parameter corresponding to `_POSIX_THREAD_STACK_MIN`.
`_SC_THREAD_THREADS_MAX`
  Inquire about the parameter corresponding to `_POSIX_THREAD_THREADS_MAX`.
`_SC_THREAD_ATTR_STACKADDR`
  Inquire about the parameter corresponding to
  a `_POSIX_THREAD_ATTR_STACKADDR`.
`_SC_THREAD_ATTR_STACKSIZE`
  Inquire about the parameter corresponding to
  `_POSIX_THREAD_ATTR_STACKSIZE`.
`_SC_THREAD_PRIORITY_SCHEDULING`
  Inquire about the parameter corresponding to `_POSIX_THREAD_PRIORITY_SCHEDULING`.
`_SC_THREAD_PRIO_INHERIT`
  Inquire about the parameter corresponding to `_POSIX_THREAD_PRIO_INHERIT`.
`_SC_THREAD_PRIO_PROTECT`
  Inquire about the parameter corresponding to `_POSIX_THREAD_PRIO_PROTECT`.
`_SC_THREAD_PROCESS_SHARED`
  Inquire about the parameter corresponding to `_POSIX_THREAD_PROCESS_SHARED`.
`_SC_2_C_DEV`
  Inquire about whether the system has the POSIX.2 C compiler command, `c89`.
`_SC_2_FORT_DEV`
  Inquire about whether the system has the POSIX.2 Fortran compiler command, `fort77`.
`_SC_2_FORT_RUN`
  Inquire about whether the system has the POSIX.2 `asa` command to interpret Fortran carriage control.
`_SC_2_LOCALEDEF`
  Inquire about whether the system has the POSIX.2 `localedef` command.
`_SC_2_SW_DEV`
  Inquire about whether the system has the POSIX.2 commands `ar`, `make`, and `strip`.
`_SC_BC_BASE_MAX`
  Inquire about the maximum value of `obase` in the `bc` utility.
`_SC_BC_DIM_MAX`
  Inquire about the maximum size of an array in the `bc` utility.
`_SC_BC_SCALE_MAX`
  Inquire about the maximum value of `scale` in the `bc` utility.
`_SC_BC_STRING_MAX`
  Inquire about the maximum size of a string constant in the `bc` utility.
`_SC_COLL_WEIGHTS_MAX`
  Inquire about the maximum number of weights that can necessarily be used in defining the collating sequence for a locale.
`_SC_EXPR_NEST_MAX`
  Inquire about the maximum number of expressions nested within parentheses when using the `expr` utility.
`_SC_LINE_MAX`
  Inquire about the maximum size of a text line that the POSIX.2 text utilities can handle.
`_SC_EQUIV_CLASS_MAX`
  Inquire about the maximum number of weights that can be assigned to an entry of the `LC_COLLATE` category ‘`order`’ keyword in a locale definition. The GNU C Library does not presently support locale definitions.
`_SC_VERSION`
  Inquire about the version number of POSIX.1 that the library and kernel support.
`_SC_2_VERSION`
  Inquire about the version number of POSIX.2 that the system utilities support.
`_SC_PAGESIZE`
  Inquire about the virtual memory page size of the machine. `getpagesize` returns the same value (see Query Memory Parameters).
`_SC_NPROCESSORS_CONF`
  Inquire about the number of configured processors.
`_SC_NPROCESSORS_ONLN`
  Inquire about the number of processors online.
`_SC_PHYS_PAGES`
  Inquire about the number of physical pages in the system.
`_SC_AVPHYS_PAGES`
  Inquire about the number of available physical pages in the system.
`_SC_ATEXIT_MAX`
  Inquire about the number of functions which can be registered as termination functions for `atexit`; see Cleanups on Exit.
`_SC_XOPEN_VERSION`
  Inquire about the parameter corresponding to `_XOPEN_VERSION`.
`_SC_XOPEN_XCU_VERSION`
  Inquire about the parameter corresponding to `_XOPEN_XCU_VERSION`.
`_SC_XOPEN_UNIX`
  Inquire about the parameter corresponding to `_XOPEN_UNIX`.
`_SC_XOPEN_REALTIME`
  Inquire about the parameter corresponding to `_XOPEN_REALTIME`.
`_SC_XOPEN_REALTIME_THREADS`
  Inquire about the parameter corresponding to `_XOPEN_REALTIME_THREADS`.
`_SC_XOPEN_LEGACY`
  Inquire about the parameter corresponding to `_XOPEN_LEGACY`.
`_SC_XOPEN_CRYPT`
  Inquire about the parameter corresponding to `_XOPEN_CRYPT`.
`_SC_XOPEN_ENH_I18N`
  Inquire about the parameter corresponding to `_XOPEN_ENH_I18N`.
`_SC_XOPEN_SHM`
  Inquire about the parameter corresponding to `_XOPEN_SHM`.
`_SC_XOPEN_XPG2`
  Inquire about the parameter corresponding to `_XOPEN_XPG2`.
`_SC_XOPEN_XPG3`
  Inquire about the parameter corresponding to `_XOPEN_XPG3`.
`_SC_XOPEN_XPG4`
  Inquire about the parameter corresponding to `_XOPEN_XPG4`.
`_SC_CHAR_BIT`
  Inquire about the number of bits in a variable of type `char`.
`_SC_CHAR_MAX`
  Inquire about the maximum value which can be stored in a variable of type `char`.
`_SC_CHAR_MIN`
  Inquire about the minimum value which can be stored in a variable of type `char`.
`_SC_INT_MAX`
  Inquire about the maximum value which can be stored in a variable of type `int`.
`_SC_INT_MIN`
  Inquire about the minimum value which can be stored in a variable of type `int`.
`_SC_LONG_BIT`
  Inquire about the number of bits in a variable of type `long int`.
`_SC_WORD_BIT`
  Inquire about the number of bits in a variable of a register word.
`_SC_MB_LEN_MAX`
  Inquire the maximum length of a multi-byte representation of a wide character value.
`_SC_NZERO`
  Inquire about the value used to internally represent the zero priority level for the process execution.
`SC_SSIZE_MAX`
  Inquire about the maximum value which can be stored in a variable of type `ssize_t`.
`_SC_SCHAR_MAX`
  Inquire about the maximum value which can be stored in a variable of type `signed char`.
`_SC_SCHAR_MIN`
  Inquire about the minimum value which can be stored in a variable of type `signed char`.
`_SC_SHRT_MAX`
  Inquire about the maximum value which can be stored in a variable of type `short int`.
`_SC_SHRT_MIN`
  Inquire about the minimum value which can be stored in a variable of type `short int`.
`_SC_UCHAR_MAX`
  Inquire about the maximum value which can be stored in a variable of type `unsigned char`.
`_SC_UINT_MAX`
  Inquire about the maximum value which can be stored in a variable of type `unsigned int`.
`_SC_ULONG_MAX`
  Inquire about the maximum value which can be stored in a variable of type `unsigned long int`.
`_SC_USHRT_MAX`
  Inquire about the maximum value which can be stored in a variable of type `unsigned short int`.
`_SC_NL_ARGMAX`
  Inquire about the parameter corresponding to `NL_ARGMAX`.
`_SC_NL_LANGMAX`
  Inquire about the parameter corresponding to `NL_LANGMAX`.
`_SC_NL_MSGMAX`
  Inquire about the parameter corresponding to `NL_MSGMAX`.
`_SC_NL_NMAX`
  Inquire about the parameter corresponding to `NL_NMAX`.
`_SC_NL_SETMAX`
  Inquire about the parameter corresponding to `NL_SETMAX`.
`_SC_NL_TEXTMAX`
  Inquire about the parameter corresponding to `NL_TEXTMAX`.