SYSCONF(3)

NAME
sysconf - get configurable system variables

LIBRARY
libc

SYNOPSIS
#include <unistd.h>
long
sysconf(int name);

DESCRIPTION
This interface is defined by p1003.1-88. A far more complete interface is available using sysctl(3).

The sysconf() function provides a method for applications to determine the current value of a configurable system limit or option variable. The name argument specifies the system variable to be queried. Symbolic constants for each name value are found in the include file <unistd.h>. Shell programmers who need access to these parameters should use the getconf(1) utility.

The available values are as follows:

_SC_ARG_MAX
    The maximum bytes of argument to execve(2).

_SC_CHILD_MAX
    The maximum number of simultaneous processes per user id.

_SC_CLK_TCK
    The frequency of the statistics clock in ticks per second.

_SC_IOV_MAX
    The maximum number of elements in the I/O vector used by readv(2), writev(2), recvmsg(2), and sendmsg(2).

_SC_NGROUPS_MAX
    The maximum number of supplemental groups.

_SC_NPROCESSORS_CONF
    The number of processors configured.

_SC_NPROCESSORS_ONLN
    The number of processors currently online.

_SC_OPEN_MAX
    One more than the maximum value the system may assign to a new file descriptor.

_SC_PAGESIZE
    The size of a system page in bytes.

_SC_PAGE_SIZE
    Equivalent to _SC_PAGESIZE.

_SC_STREAM_MAX
    The minimum maximum number of streams that a process may have open at any one time.

_SC_TZNAME_MAX
    The minimum maximum number of types supported for the name of a timezone.

_SC_JOB_CONTROL
    Return 1 if job control is available on this system, otherwise -1.

_SC_SAVED_IDS
    Returns 1 if saved set-group and saved set-user ID is available, otherwise -1.

_SC_VERSION
    The version of p1003.1 with which the system attempts to comply.

_SC_BC_BASE_MAX
    The maximum ibase/obase values in the bc(1) utility.

_SC_BC_DIM_MAX
    The maximum array size in the bc(1) utility.

_SC_BC_SCALE_MAX
    The maximum scale value in the bc(1) utility.

_SC_BC_STRING_MAX
    The maximum string length in the bc(1) utility.

_SC_COLL_WEIGHTS_MAX
    The maximum number of weights that can be assigned to any entry of the LC_COLLATE order keyword in the locale definition file.

_SC_EXPR_NEST_MAX
    The maximum number of expressions that can be nested within parenthesis by the expr(1) utility.

_SC_LINE_MAX
    The maximum length in bytes of a text-processing utility's input line.

_SC_RE_DUP_MAX
    The maximum number of repeated occurrences of a regular expression permitted when using interval notation.

_SC_2_VERSION
    The version of p1003.2 with which the system attempts to comply.

_SC_2_C_BIND
    Return 1 if the system's C-language development facilities support the C-Language Bindings Option, otherwise -1.

_SC_2_C_DEV
    Return 1 if the system supports the C-Language Development Utilities Option, otherwise -1.

_SC_2_CHAR_TERM
    Return 1 if the system supports at least one terminal type capable of all operations described in p1003.2, otherwise -1.

_SC_2_FORT_DEV
    Return 1 if the system supports the FORTRAN Development Utilities Option, otherwise -1.

_SC_2_FORT_RUN
    Return 1 if the system supports the FORTRAN Runtime Utilities Option, otherwise -1.

_SC_2_LOCALEDEF
    Return 1 if the system supports the creation of locales, otherwise -1.

_SC_2_SW_DEV
    Return 1 if the system supports the Software Development Utilities Option, otherwise -1.

_SC_2_UPE
    Return 1 if the system supports the User Portability Utilities Option, otherwise -1.

_SC_AIO_LISTIO_MAX
    Maximum number of I/O operations in a single list I/O call supported.

_SC_AIO_MAX
    Maximum number of outstanding asynchronous I/O operations supported.

_SC_AIO_PRIO_DELTA_MAX
    The maximum amount by which a process can decrease its asynchronous I/O priority level from its own scheduling priority.

_SC_DELAYTIMER_MAX
    Maximum number of timer expiration overruns.

_SC_MQ_OPEN_MAX
    The maximum number of open message queue descriptors a process may hold.

_SC_RTSIG_MAX
    Maximum number of realtime signals reserved for application use.

_SC_SEM_NSEMS_MAX
    Maximum number of semaphores that a process may have.

_SC_SEM_VALUE_MAX
    The maximum value a semaphore may have.

_SC_SIGQUEUE_MAX
    Maximum number of queued signals that a process may send and have pending at the receiver(s) at any time.

_SC_TIMER_MAX
    Maximum number of timers per process supported.

_SC_GETGR_R_SIZE_MAX
    Suggested initial value for the size of the group entry buffer.

_SC_GETPW_R_SIZE_MAX
    Suggested initial value for the size of the password entry buffer.

_SC_HOST_NAME_MAX
    Maximum length of a host name (not including the terminating null) as returned from the gethostname() function.

_SC_LOGIN_NAME_MAX
    Maximum length of a login name.

_SC_THREAD_STACK_MIN
    Minimum size in bytes of thread stack storage.

_SC_THREAD_THREADS_MAX
    Maximum number of threads that can be created per process.

_SC_TTY_NAME_MAX
    Maximum length of terminal device name.

_SC_SYMLOOP_MAX
    Maximum number of symbolic links that can be reliably traversed in the resolution of a pathname in the absence of a loop.

_SC_ATEXIT_MAX
    Maximum number of functions that may be registered with atexit().

_SC_XOPEN_VERSION
    An integer value greater than or equal to 4, indicating the version of the X/Open Portability Guide to which this system conforms.

_SC_XOPEN_XCU_VERSION
    An integer value indicating the version of the XCU Specification to which this system conforms.

These values also exist, but may not be standard:

_SC_CPUSET_SIZE
    Size of the kernel cpuset.

_SC_PHYS_PAGES
    The number of pages of physical memory. Note that it is possible that the product of this value and the value of _SC_PAGESIZE will overflow a long in some configurations on a 32bit machine.

RETURN VALUES
If the call to sysconf() is not successful, -1 is returned and errno is set appropriately. Otherwise, if the variable is associated with functionality that is not supported, -1 is returned and errno is not modified. Otherwise, the current variable value is returned.

ERRORS
The sysconf() function may fail and set errno for any of the errors specified for the library function sysctl(3). In addition, the following error may be reported:

[EINVAL]
    The value of the name argument is invalid.

SEE ALSO
getconf(1), pathconf(2), confstr(3), sysctl(3)

STANDARDS
Except for the fact that values returned by sysconf() may change over the lifetime of the calling process, this function conforms to p1003.1-88.

HISTORY
The sysconf() function first appeared in 4.4BSD.

BUGS
The value for _SC_STREAM_MAX is a minimum maximum, and required to be the same as ANSI C's FOPEN_MAX, so the returned value is a ridiculously small and misleading number.