#include <unistd.h>long sysconf(int name);
The sysinfo(2) and confstr(3C) routines provide a similar class of configuration information.
The following table lists the minimal set of system variables from limits.h and unistd.h that can be returned by sysconf, and the symbolic constants, defined in unistd.h that are the corresponding values used for name.
| Name | Return value (minimum) |
|---|---|
| _SC_ARG_MAX | ARG_MAX |
| _SC_BC_BASE_MAX | BC_BASE_MAX |
| _SC_BC_DIM_MAX | BC_DIM_MAX |
| _SC_BC_SCALE_MAX | BC_SCALE_MAX |
| _SC_BC_STRING_MAX | BC_STRING_MAX |
| _SC_CHILD_MAX | CHILD_MAX |
| _SC_CACHE_LINE | The worst-case (largest) cache line size of the various levels of memory cache that are present on the machine, as reported by the Platform Support Module via the topology. A default value of 32 is assigned if the topology provides no information. |
| _SC_CLK_TCK | CLK_TCK |
| _SC_COLL_WEIGHTS_MAX | COLL_WEIGHTS_MAX |
| _SC_EXPR_NEST_MAX | EXPR_NEST_MAX |
| _SC_IOV_MAX | IOV_MAX |
| _SC_LINE_MAX | LINE_MAX |
| _SC_JOB_CONTROL | _POSIX_JOB_CONTROL |
| _SC_LOGNAME_MAX | LOGNAME_MAX |
| _SC_NACLS_MAX | _CONFIG_NACLS_MAX |
| _SC_NGROUPS_MAX | NGROUPS_MAX |
| _SC_OPEN_MAX | OPEN_MAX |
| _SC_PAGESIZE | PAGESIZE |
| _SC_PASS_MAX | PASS_MAX |
| _SC_SAVED_IDS | _POSIX_SAVED_IDS |
| _SC_VERSION | _POSIX_VERSION |
| _SC_XOPEN_VERSION | _XOPEN_VERSION |
| _SC_XOPEN_XCU_VERSION | _XOPEN_XCU_VERSION |
| _SC_BC_BASE_MAX | _POSIX2_BC_BASE_MAX |
| _SC_BD_DIM_MAX | _POSIX2_BC_DIM_MAX |
| _SC_BC_SCALE_MAX | _POSIX2_BC_SCALE_MAX |
| _SC_BC_STRING_MAX | _POSIX2_BC_STRING_MAX |
| _SC_COLL_WEIGHTS_MAX | _POSIX2_COLL_WEIGHTS_MAX |
| _SC_EXPR_NEST_MAX | _POSIX2_EXPR_NEST_MAX |
| _SC_STREAM_MAX | _POSIX2_STREAM_MAX |
| _SC_RE_DUP_MAX | _RE_DUP_MAX |
| _SC_LINE_MAX | _POSIX2_LINE_MAX |
| _SC_TZNAME_MAX | TZNAME_MAX |
| _SC_LINE_MAX | 1 |
| _SC_XOPEN_CRYPT | 1 |
| _SC_2_C_VERSION | _POSIX2_C_VERSION |
| _SC_2_CHAR_TERM | _POSIX2_CHAR_TERM |
| _SC_2_FORT_RUN | _POSIX2_FORT_RUN |
| _SC_2_UPE | _POSIX2_UPE |
| _SC_XOPEN_ENH_I18N | _POSIX2_XOPEN_ENH_I18N |
| _SC_2_LOCALEDEF | _POSIX2_LOCALEDEF |
| _SC_2_VERSION | _POSIX2_VERSION |
| _SC_NCGS_CONF | Number of configured CPU-Groups |
| _SC_NCGS_ONLN | Number of online CPU-Groups |
| _SC_MAX_CPUS_PER_CG | Maximum number of processors on a CPU-Group (which may be greater than the maximum number of processors on a specific CPU-Group if the CPU-Groups are not all symmetric). |
| _SC_CG_SIMPLE_IMPL | _CG_SIMPLE_IMPL |
Name Return value (minimum)
_SC_ARG_MAX ARG_MAX
_SC_BC_BASE_MAX BC_BASE_MAX
_SC_BC_DIM_MAX BC_DIM_MAX
_SC_BC_SCALE_MAX BC_SCALE_MAX
_SC_BC_STRING_MAX BC_STRING_MAX
_SC_CHILD_MAX CHILD_MAX
_SC_CACHE_LINE The worst-case (largest) cache
line size of the various levels
of memory cache that are present
on the machine, as reported by
the Platform Support Module via
the topology. A default value
of 32 is assigned if the
topology provides no
information.
_SC_CLK_TCK CLK_TCK
_SC_COLL_WEIGHTS_MAX COLL_WEIGHTS_MAX
_SC_EXPR_NEST_MAX EXPR_NEST_MAX
_SC_IOV_MAX IOV_MAX
_SC_LINE_MAX LINE_MAX
_SC_JOB_CONTROL _POSIX_JOB_CONTROL
_SC_LOGNAME_MAX LOGNAME_MAX
_SC_NACLS_MAX _CONFIG_NACLS_MAX
_SC_NGROUPS_MAX NGROUPS_MAX
_SC_OPEN_MAX OPEN_MAX
_SC_PAGESIZE PAGESIZE
_SC_PASS_MAX PASS_MAX
_SC_SAVED_IDS _POSIX_SAVED_IDS
_SC_VERSION _POSIX_VERSION
_SC_XOPEN_VERSION _XOPEN_VERSION
_SC_XOPEN_XCU_VERSION _XOPEN_XCU_VERSION
_SC_BC_BASE_MAX _POSIX2_BC_BASE_MAX
_SC_BD_DIM_MAX _POSIX2_BC_DIM_MAX
_SC_BC_SCALE_MAX _POSIX2_BC_SCALE_MAX
_SC_BC_STRING_MAX _POSIX2_BC_STRING_MAX
_SC_COLL_WEIGHTS_MAX _POSIX2_COLL_WEIGHTS_MAX
_SC_EXPR_NEST_MAX _POSIX2_EXPR_NEST_MAX
_SC_STREAM_MAX _POSIX2_STREAM_MAX
_SC_RE_DUP_MAX _RE_DUP_MAX
_SC_LINE_MAX _POSIX2_LINE_MAX
_SC_TZNAME_MAX TZNAME_MAX
_SC_LINE_MAX 1
_SC_XOPEN_CRYPT 1
_SC_2_C_VERSION _POSIX2_C_VERSION
_SC_2_CHAR_TERM _POSIX2_CHAR_TERM
_SC_2_FORT_RUN _POSIX2_FORT_RUN
_SC_2_UPE _POSIX2_UPE
_SC_XOPEN_ENH_I18N _POSIX2_XOPEN_ENH_I18N
_SC_2_LOCALEDEF _POSIX2_LOCALEDEF
_SC_2_VERSION _POSIX2_VERSION
_SC_NCGS_CONF Number of configured CPU-Groups
_SC_NCGS_ONLN Number of online CPU-Groups
_SC_MAX_CPUS_PER_CG Maximum number of processors on
a CPU-Group (which may be
greater than the maximum number
of processors on a specific
CPU-Group if the CPU-Groups are
not all symmetric).
_SC_CG_SIMPLE_IMPL _CG_SIMPLE_IMPL
The value of CLK_TCK may be variable and it should not be assumed that CLK_TCK is a compile-time constant. The value of CLK_TCK is the same as the value of sysconf(_SC_CLK_TCK).
sysconf can also return the following values:
| Name | Return value |
|---|---|
| _SC_ATEXIT_MAX | Maximum number of atexit functions that can be registered |
| _SC_NPROCESSORS_CONF | Number of configured processors |
| _SC_NPROCESSORS_ONLN | Number of online processors |
| _SC_NPROCESSES | Number of processes per real user id |
| _SC_PAGE_SIZE | Size in bytes of physical page |
| _SC_PAGESIZE | Size in bytes of physical page |
| _SC_SYSTEM_ID | Persistent, system-generated identifier |
Name Return value
_SC_ATEXIT_MAX Maximum number of atexit functions that
can be registered
_SC_NPROCESSORS_CONF Number of configured processors
_SC_NPROCESSORS_ONLN Number of online processors
_SC_NPROCESSES Number of processes per real user id
_SC_PAGE_SIZE Size in bytes of physical page
_SC_PAGESIZE Size in bytes of physical page
_SC_SYSTEM_ID Persistent, system-generated identifier
The following variables return 1, that is, the feature is supported:
The following variables return -1 if the feature is not supported.