sysconf() — Determine system configuration options

int name

Specifies the system configuration option to be obtained. The value of name can be any one of the following set of symbols defined in the unistd.h header file, each corresponding to a system configuration option:

The following are available when _POSIX_SOURCE is defined.

_SC_ARG_MAX

Represents ARG_MAX, as defined by the values returned by sysconf(), the maximum number of bytes of arguments and environment data that can be passed in an exec function.

_SC_CHILD_MAX

Represents CHILD_MAX, as defined by the values returned by sysconf(), the maximum number of processes that a real user ID (UID) may have running simultaneously.

_SC_CLK_TCK

Represents the CLK_TCK macro defined in the time.h header file: the number of clock ticks in a second.

_SC_JOB_CONTROL

Represents the _POSIX_JOB_CONTROL macro that can be defined in the unistd.h header file. This indicates that certain job control operations are implemented by this version of the operating system. If _POSIX_JOB_CONTROL is defined, various functions (for example, setpgid()) have more functionality than when the macro is not defined.

_SC_NGROUPS_MAX

Represents NGROUPS_MAX, as defined by the values returned by sysconf(), the maximum number of supplementary group IDs (GIDs) that can be associated with a process.

_SC_OPEN_MAX

Represents OPEN_MAX, as defined by the values returned by sysconf(), the maximum number of files that a single process can have open at one time.

_SC_SAVED_IDS

Represents the _POSIX_SAVED_IDS macro, which may be defined in unistd.h header file, indicating that this POSIX implementation has a saved set UID and a saved set GID. This symbol affects the behavior of such functions as setuid() and setgid().

_SC_STREAM_MAX

Represents the _STREAM_MAX macro, which may be defined in the unistd.h header file, indicating the maximum number of streams that a process can have open at one time.

_SC_THREADS_MAX_NP

Represents the THREAD_MAX macro, as defined by the values returned by sysconf(), the maximum number of concurrent threads processed by pthread_create(), including running, queued, and exited undetached threads in the caller's process.

_SC_THREAD_TASKS_MAX_NP

Represents the THREAD_TASKS_MAX macro, as defined by the values returned by sysconf(), the maximum number of MVS™ tasks simultaneously in use for threads processed by pthread_create() in the caller's process.

_SC_TTY_GROUP

Retrieves the group number associated with the TTYGROUP() initialization parameter.

_SC_TZNAME_MAX

Represents the _TZNAME_MAX macro, which may be defined in the unistd.h header file, indicating the maximum length of the name of a time zone.

_SC_VERSION

Represents the _POSIX_VERSION macro, which will be defined in the unistd.h header file, indicating the version of the POSIX.1 standard that the system conforms to.

In addition to the symbols exposed by _POSIX_SOURCE, the following are visible when _XOPEN_SOURCE is defined:

_SC_XOPEN_CRYPT

Represents _XOPEN_CRYPT, the implementation supports the X/Open Encryption Option Group.

_SC_XOPEN_VERSION

Represents _XOPEN_VERSION, integer value indicating version of the X/Open Portability Guide to which the implementation conforms.

_SC_PASS_MAX

Represents PASS_MAX, as defined by the values returned by sysconf(), the maximum number of bytes allowed in a password, PassTicket, or password phrase.

Note:

It was part of the Legacy Feature in Single UNIX Specification, Version 2, but has been withdrawn and is not supported as part of Single UNIX Specification, Version 3.

If it is necessary to continue using this function in an application written for Single UNIX Specification, Version 3, define the feature test macro _UNIX03_WITHDRAWN before including any standard system headers. The macro exposes all interfaces and symbols removed in Single UNIX Specification, Version 3.

In addition to the symbols exposed by _XOPEN_SOURCE, the following are visible when _XOPEN_SOURCE_EXTENDED is defined to be 1:

_SC_PAGE_SIZE

Returns the current page size in bytes.

_SC_PAGESIZE

Returns the current page size in bytes.

In addition to the symbols exposed by _POSIX_SOURCE, the following are visible when _POSIX_C_SOURCE is defined to be 2:

_SC_2_C_BIND

Represents _POSIX2_C_BIND, the implementation supports the C-Language Binding option.

_SC_2_C_DEV

Represents _POSIX2_C_DEV, the implementation supports the C-Language Development Utilities option.

_SC_2_LOCALEDEF

Represents _POSIX2_LOCALEDEF, the implementation supports the creation of locales by the localedef utility.

_SC_2_UPE

Represents _POSIX2_UPE, the implementation supports the User Portability Utilities option. .

_SC_2_VERSION

Represents _POSIX2_VERSION, integer value indicating version of the Shell and Utilities to which the implementation conforms.

In addition to the symbols exposed by _POSIX_C_SOURCE defined to be 2, the following are visible when _POSIX_C_SOURCE is defined to be 200112L:

_SC_HOST_NAME_MAX

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

_SC_IPV6

Represents _POSIX_IPV6, the implementation supports the IPv6 option.

_SC_LOGIN_NAME_MAX

Represents LOGIN_NAME_MAX, Maximum length of a login name.

_SC_READER_WRITER_LOCKS

Represents _POSIX_READER_WRITER_LOCKS, the implementation supports the Read-Write Locks option. This is always set to a value greater than zero if the Threads option is supported.

_SC_REGEXP

Represents _POSIX_REGEXP, the implementation supports the Regular Expression Handling option.

_SC_SHELL

Represents _POSIX_SHELL, the implementation supports the POSIX shell.

_SC_SYMLOOP_MAX

Represents SYMLOOP_MAX, maximum number of symbolic links that can be reliably traversed in the resolution of a path name in the absence of a loop.

_SC_THREAD_ATTR_STACKSIZE

Represents _POSIX_THREAD_ATTR_STACKSIZE, the implementation supports the Thread Stack Size Attribute option.

_SC_THREAD_KEYS_MAX

Represents PTHREAD_KEYS_MAX, maximum number of data keys that can be created by a process.

_SC_THREAD_PROCESS_SHARED

Represents _POSIX_THREAD_PROCESS_SHARED, the implementation supports the Thread Process-Shared Synchronization option.

_SC_THREAD_SAFE_FUNCTIONS

Represents _POSIX_THREAD_SAFE_FUNCTIONS, the implementation supports the Thread-Safe Functions option.

_SC_THREAD_STACK_MIN

Represents PTHREAD_STACK_MIN, minimum size in bytes of thread stack storage.

_SC_THREAD_THREADS_MAX

Represents PTHREAD_THREADS_MAX, maximum number of threads that can be created per process.

_SC_THREADS

Represents _POSIX_THREADS, the implementation supports the Threads option.

_SC_TTY_NAME_MAX

Represents TTY_NAME_MAX, maximum length of terminal device name.

_SC_V6_ILP32_OFF32

Represents _POSIX_V6_ILP32_OFF32, the implementation provides a C-language compilation environment with 32-bit int, long, pointer, and off_t types.

_SC_V6_ILP32_OFFBIG

Represents _POSIX_V6_ILP32_OFFBIG, the implementation provides a C-language compilation environment with 32-bit int, long, and pointer types and an off_t type using at least 64 bits.

_SC_V6_LP64_OFF64

Represents _POSIX_V6_LP64_OFF64, the implementation provides a C-language compilation environment with 32-bit int and 64-bit long, pointer, and off_t types.

_SC_V6_LPBIG_OFFBIG

Represents _POSIX_V6_LPBIG_OFFBIG, the implementation provides a C-language compilation environment with an int type using at least 32 bits and long, pointer, and off_t types using at least 64 bits.

_SC_XOPEN_LEGACY

Represents _XOPEN_LEGACY, the implementation supports the Legacy Option Group.

Error Code

Description

EINVAL

The value specified for the name argument is incorrect.

⁄* CELEBS61

   This example determines the value of ARG_MAX.

 *⁄
#define _POSIX_SOURCE
#include <stdio.h>
#include <unistd.h>
#include <errno.h>

main() {
  long result;

  errno = 0;
  puts("examining ARG_MAX limit");
  if ((result = sysconf(_SC_ARG_MAX)) == -1)
    if (errno == 0)
      puts("ARG_MAX is not supported.");
    else perror("sysconf() error");
  else
    printf("ARG_MAX is %ld\n", result);
}

examining ARG_MAX limit
ARG_MAX is 1048576