sysconf - Get configurable system variables
#include <unistd.h>
long sysconf(
int name );
Standard C Library (libc)
Interfaces documented on this reference page conform to
industry standards as follows:
sysconf(): POSIX.1c, XSH4.2
Refer to the standards(5) reference page for more information
about industry standards and associated tags.
Specifies the system variable to be queried.
The sysconf() function provides a method for the application
to determine the current value of a configurable system
limit or whether optional features are supported.
The following is a list of system variables that are
returned by the sysconf() function, and the symbolic constants
(shown in parentheses) that are the corresponding
values used for the name parameter. The variables come
from either the limits.h, unistd.h, or time.h (for
CLK_TCK) header file and the symbolic constants are
defined in unistd.h.
[Tru64 UNIX] Integer value indicating the revision of the
AES to which the implementation is compliant. Maximum
length, in bytes, of the arguments for one of the exec
functions, including environment data. [XSH4.2] Maximum
number of functions that can be registered with atexit()
per process. (_SC_ATEXIT_MAX) Maximum value allowed for
the obase variable with the bc command. Maximum number of
elements permitted in an array by the bc command. Maximum
value allowed for the scale variable with the bc command.
Maximum length of string constants accepted by the bc command.
Maximum number of simultaneous processes for each
real user ID. Number of clock ticks per second. The value
of CLK_TCK may be variable, and it should not be assumed
that CLK_TCK is a compile-time constant. Maximum number
of weights that can be assigned to an entry in the LC_COLLATE
locale-dependent information in a locale-definition
file Maximum number of expressions that can be nested
within parentheses by the expr command. [XSH4.2] Maximum
number of iovec structures that one process has available
for use with readv() or writev(). Maximum length, in
bytes, of a command's input line (either standard input or
another file) when the utility is described as processing
text files. The length includes room for the trailing newline
character. Maximum number of simultaneous supplementary
group IDs for each process. Maximum number of files
that one process can have open at one time.
[Tru64 UNIX] In some cases, the per-process soft
descriptor limit is returned instead of the
OPEN_MAX value. [XSH4.2] Page size granularity
for memory regions. [XSH4.2] Page size granularity
for memory regions. Maximum number of characters
returned by getpass(), (not including the terminating
null character). The variable has a value
of 1 if the system supports job control; otherwise,
-1 is returned. [POSIX] The variable has a value
of 1 if the system supports POSIX reentrant functions;
otherwise, -1 is returned. The variable has
a value of 1 if each process has a saved set user
ID and a saved set group ID; otherwise, -1 is
returned. [POSIX] The variable has a value of 1
if the system supports the POSIX.1 Threads option;
otherwise, -1 is returned. [POSIX] The variable
has a value of 1 if the system supports the POSIX.1
Threads Stack Size attribute option; otherwise, -1
is returned. Date of approval of the most current
version of the POSIX 1 standard that the system
supports. The date is a 6-digit number, with the
first 4 digits signifying the year and the last 2
digits the month. Different versions of the POSIX 1
standard are periodically approved by the IEEE
Standards Board, and the date of approval is used
to distinguish between different versions. If
_POSIX_VERSION is defined, it is returned; otherwise,
-1 is returned. The variable has a value of
1 if the system supports the C language binding
from POSIX 2; otherwise, -1 is returned. The variable
has a value of 1 if the system supports the
optional C Language Development Utilities from
POSIX 2; otherwise, -1 is returned. Date of
approval of the most current version of the POSIX 2
ISO C standard that the system supports. The date
is a 6-digit number, with the first 4 digits signifying
the year and the last 2 digits the month.
Different versions of the POSIX 2 ISO C standard
are periodically approved by the IEEE Standards
Board, and the date of approval is used to distinguish
between different versions. The variable has
a value of 1 if the system supports at least one
terminal; otherwise -1 is returned. The variable
has a value of 1 if the system supports the FORTRAN
Development Utilities Option from POSIX 2; otherwise,
-1 is returned. The variable has a value of
1 if the system supports the FORTRAN Runtime Utilities
Option from POSIX 2; otherwise, -1 is
returned. The variable has a value of 1 if the
system supports the creation of new locales with
the localedef command; otherwise, -1 is returned.
The variable has a value of 1 if the system supports
the Software Development Utilities Option
from POSIX 2; otherwise, -1 is returned. The variable
has a value of 1 if the system supports the
User Portability Environment Option from POSIX 2;
otherwise, -1 is returned. Date of approval of the
most current version of the POSIX 2 standard that
the system supports. The date is a 6-digit number,
with the first 4 digits signifying the year and the
last 2 digits the month. Different versions of the
POSIX 2 standard are periodically approved by the
IEEE Standards Board, and the date of approval is
used to distinguish between different versions.
Maximum number of repeated occurrences of a regular
expression permitted when using the interval-notation
parameters, such as the m and n parameters
with the ed command. [POSIX] Maximum number of
outstanding asynchronous I/O operations.
[POSIX] Maximum number of I/O operations in a single
list I/O call. [POSIX] The variable has a
value of 1 if the system supports the POSIX Asynchronous
Input and Output option; otherwise -1 is
returned. [POSIX] Maximum number of timer expiration
overruns. [POSIX] The variable has a value
of 1 if the system supports the POSIX.1 File Synchronization
option; otherwise -1 is returned.
[POSIX] Maximum size of data buffers for getgrgid_r
and getgrnam_r functions. [POSIX] Maximum
size of data buffers for getpwuid_r and getpwnam_r
functions. [POSIX] Maximum number of I/O operations
in a single list I/O call. Avoid using
_SC_LISTIO_AIO_MAX, which is only retained for
backward compatibility. Use only the CAEUNIX98-compliant
_SC_AIO_LISTIO_MAX operation.
Size in bytes of storage required for a login name,
including the terminating null character.
[POSIX] The variable has a value of 1 if the system
supports the POSIX.1 Memory Mapped Files
option; otherwise -1 is returned. [POSIX] The
variable has a value of 1 if the system supports
the POSIX.1 Process Memory Locking option; otherwise
-1 is returned. [POSIX] The variable has a
value of 1 if the system supports the POSIX.1 Range
Memory Locking option; otherwise -1 is returned.
[POSIX] The variable has a value of 1 if the system
supports the POSIX.1 Memory Protection option;
otherwise -1 is returned. [POSIX] The variable
has a value of 1 if the system supports the POSIX.1
Message Passing option; otherwise -1 is returned.
[POSIX] Maximum number of open message queue
descriptors a process may hold. [POSIX] Maximum
number of message priorities. [POSIX] The variable
has a value of 1 if the system supports the
POSIX.1 Prioritized Input and Output option; otherwise
-1 is returned. [POSIX] The variable has a
value of 1 if the system supports the POSIX.1 Process
Scheduling option; otherwise -1 is returned.
[POSIX] The variable has a value of 1 if the system
supports the POSIX.1 Realtime Signals Extension
option; otherwise -1 is returned. [POSIX] Maximum
number of realtime signals reserved for application
use. [POSIX] The variable has a value of 1 if the
system supports the POSIX.1 Shared Memory Objects
option; otherwise -1 is returned. [POSIX] The
variable has a value of 1 if the system supports
the POSIX.1 Semaphores option; otherwise -1 is
returned. [POSIX] Maximum number of semaphores
that a process may have. [POSIX] Maximum value a
semaphore can have. [POSIX] Maximum number of
queued signals that a process may send and have
pending at the receiver(s) at any time.
[POSIX] The variable has a value of 1 if the system
supports the POSIX.1 Synchronized Input and
Output option; otherwise -1 is returned.
[POSIX] The variable has a value of 1 if the system
supports the POSIX.1 Thread Stack Address
Attribute option; otherwise -1 is returned.
[POSIX] Maximum number of attempts made to destroy
a thread's thread-specific data values on thread
exit. [POSIX] Maximum number of data keys that
can be created per-process. [POSIX] The variable
has a value of 1 if the system supports the POSIX.1
Priority Inheritance option; otherwise -1 is
returned. [POSIX] The variable has a value of 1
if the system supports the POSIX.1 Priority Protection
option; otherwise -1 is returned.
[POSIX] The variable has a value of 1 if the system
supports the POSIX.1 Thread Execution Scheduling
option; otherwise -1 is returned. [POSIX] The
variable has a value of 1 if the system supports
the POSIX.1 Process-Shared Synchronization option;
otherwise -1 is returned. [POSIX] The variable
has a value of 1 if the system supports the POSIX.1
Thread-Safe Functions option; otherwise -1 is
returned. [POSIX] Minimum size in bytes of thread
stack storage. [POSIX] Maximum number of threads
that can be created per process. [POSIX] Maximum
number of timers per process. [POSIX] The variable
has a value of 1 if the system supports the
POSIX.1 Timers option; otherwise -1 is returned.
Maximum length of terminal device name. Number of
streams that one process can have open at one time.
Maximum number of bytes supported for the name of a
time zone (not the length of the TZ environmental
variable). The variable has a value of 1 if the
system supports the X/Open Encryption Feature
Group; otherwise, -1 is returned. The variable has
a value of 1 if the system supports the X/Open
Enhanced Internationalization Feature Group; otherwise,
-1 is returned. The variable has a value of
1 if the system supports the X/Open Shared Memory
Feature Group; otherwise, -1 is returned.
[XSH4.2] The variable has a value of 1 if the system
supports the X/Open UNIX Feature Group; otherwise,
-1 is returned. Integer indicating the most
current version of the X/Open standard that the
system supports. Integer indicating the most current
version of the X/Open standard for Commands
and Utilities that the system supports.
[Tru64 UNIX] The following values of name are supported
as part of the System V Environment for compliance with
the System V Release 4.0 with Multiprocessing (SVR4.0MP)
standards: Number of processors in the system. Number of
processors currently online.
If the name parameter is an invalid value, the sysconf()
function returns a value of -1, and sets errno to indicate
the error. If the variable corresponding to name is undefined,
the sysconf() function returns a value of -1 without
changing the value of errno.
If the following condition occurs, the sysconf() function
sets errno to the corresponding value: The value of the
name parameter is invalid.
Functions: pathconf(2)
Commands: getconf(1)
Standards: standards(5)
sysconf(3)
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