---
name: "sysconf"
section: "3"
platform: "macos"
package: "Libc"
version: "1752.120.2"
release: "macOS 26.5"
platforms: ["linux", "freebsd", "macos"]
url: "https://new.carta.tech/sysconf/3"
---

# sysconf(3)

get configurable system variables

## NAME

**sysconf** – get configurable system variables

## LIBRARY

Standard C Library (libc, -lc)

## SYNOPSIS

**#include \<unistd.h\>**

*long*\

**sysconf**(*int name*);

## DESCRIPTION

This interface is defined by IEEE Std 1003.1-1988 (“POSIX.1”). A far more complete interface is available using [sysctl(3)](/sysctl/3.md).

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)](/getconf/1.md) utility.

The available values are as follows:

- \_SC\_ARG\_MAX

  The maximum bytes of argument to [execve(2)](/execve/2.md).

- \_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)](/readv/2.md), [writev(2)](/writev/2.md), [recvmsg(2)](/recvmsg/2.md), and [sendmsg(2)](/sendmsg/2.md).

- \_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

  The maximum number of open files per user id.

- \_SC\_PAGESIZE

  The size of a system page in bytes.

- \_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 IEEE Std 1003.1 (“POSIX.1”) with which the system attempts to comply.

- \_SC\_BC\_BASE\_MAX

  The maximum ibase/obase values in the [bc(1)](/bc/1.md) utility.

- \_SC\_BC\_DIM\_MAX

  The maximum array size in the [bc(1)](/bc/1.md) utility.

- \_SC\_BC\_SCALE\_MAX

  The maximum scale value in the [bc(1)](/bc/1.md) utility.

- \_SC\_BC\_STRING\_MAX

  The maximum string length in the [bc(1)](/bc/1.md) 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)](/expr/1.md) 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 IEEE Std 1003.2 (“POSIX.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 IEEE Std 1003.2 (“POSIX.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.

These values also exist, but may not be standard:

- \_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)](/sysctl/3.md). In addition, the following error may be reported:

- \[EINVAL\]

  The value of the *name* argument is invalid.

## SEE ALSO

[getconf(1)](/getconf/1.md), [pathconf(2)](/pathconf/2.md), [confstr(3)](/confstr/3.md), [sysctl(3)](/sysctl/3.md)

## STANDARDS

Except for the fact that values returned by **sysconf**() may change over the lifetime of the calling process, this function conforms to IEEE Std 1003.1-1988 (“POSIX.1”).

## 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.