@node System Configuration, Cryptographic Functions, System Management, Top

@c %MENU% Parameters describing operating system limits

@chapter System Configuration Parameters

The functions and macros listed in this chapter give information about

configuration parameters of the operating system---for example, capacity

limits, presence of optional POSIX features, and the default path for

executable files (@pxref{String Parameters}).

@menu

* General Limits::           Constants and functions that describe

				various process-related limits that have

				one uniform value for any given machine.

* System Options::           Optional POSIX features.

* Version Supported::        Version numbers of POSIX.1 and POSIX.2.

* Sysconf::                  Getting specific configuration values

                                of general limits and system options.

* Minimums::                 Minimum values for general limits.

* Limits for Files::         Size limitations that pertain to individual files.

                                These can vary between file systems

                                or even from file to file.

* Options for Files::        Optional features that some files may support.

* File Minimums::            Minimum values for file limits.

* Pathconf::                 Getting the limit values for a particular file.

* Utility Limits::           Capacity limits of some POSIX.2 utility programs.

* Utility Minimums::         Minimum allowable values of those limits.

* String Parameters::        Getting the default search path.

@end menu

@node General Limits

@section General Capacity Limits

@cindex POSIX capacity limits

@cindex limits, POSIX

@cindex capacity limits, POSIX

The POSIX.1 and POSIX.2 standards specify a number of parameters that

describe capacity limitations of the system.  These limits can be fixed

constants for a given operating system, or they can vary from machine to

machine.  For example, some limit values may be configurable by the

system administrator, either at run time or by rebuilding the kernel,

and this should not require recompiling application programs.

@pindex limits.h

Each of the following limit parameters has a macro that is defined in

@file{limits.h} only if the system has a fixed, uniform limit for the

parameter in question.  If the system allows different file systems or

files to have different limits, then the macro is undefined; use

@code{sysconf} to find out the limit that applies at a particular time

on a particular machine.  @xref{Sysconf}.

Each of these parameters also has another macro, with a name starting

with @samp{_POSIX}, which gives the lowest value that the limit is

allowed to have on @emph{any} POSIX system.  @xref{Minimums}.

@cindex limits, program argument size

@deftypevr Macro int ARG_MAX

@standards{POSIX.1, limits.h}

If defined, the unvarying maximum combined length of the @var{argv} and

@var{environ} arguments that can be passed to the @code{exec} functions.

@end deftypevr

@cindex limits, number of processes

@deftypevr Macro int CHILD_MAX

@standards{POSIX.1, limits.h}

If defined, the unvarying maximum number of processes that can exist

with the same real user ID at any one time.  In BSD and GNU, this is

controlled by the @code{RLIMIT_NPROC} resource limit; @pxref{Limits on

Resources}.

@end deftypevr

@cindex limits, number of open files

@deftypevr Macro int OPEN_MAX

@standards{POSIX.1, limits.h}

If defined, the unvarying maximum number of files that a single process

can have open simultaneously.  In BSD and GNU, this is controlled

by the @code{RLIMIT_NOFILE} resource limit; @pxref{Limits on Resources}.

@end deftypevr

@deftypevr Macro int STREAM_MAX

@standards{POSIX.1, limits.h}

If defined, the unvarying maximum number of streams that a single

process can have open simultaneously.  @xref{Opening Streams}.

@end deftypevr

@cindex limits, time zone name length

@deftypevr Macro int TZNAME_MAX

@standards{POSIX.1, limits.h}

If defined, the unvarying maximum length of a time zone name.

@xref{Time Zone Functions}.

@end deftypevr

These limit macros are always defined in @file{limits.h}.

@cindex limits, number of supplementary group IDs

@deftypevr Macro int NGROUPS_MAX

@standards{POSIX.1, limits.h}

The maximum number of supplementary group IDs that one process can have.

The value of this macro is actually a lower bound for the maximum.  That

is, you can count on being able to have that many supplementary group

IDs, but a particular machine might let you have even more.  You can use

@code{sysconf} to see whether a particular machine will let you have

more (@pxref{Sysconf}).

@end deftypevr

@deftypevr Macro ssize_t SSIZE_MAX

@standards{POSIX.1, limits.h}

The largest value that can fit in an object of type @code{ssize_t}.

Effectively, this is the limit on the number of bytes that can be read

or written in a single operation.

This macro is defined in all POSIX systems because this limit is never

configurable.

@end deftypevr

@deftypevr Macro int RE_DUP_MAX

@standards{POSIX.2, limits.h}

The largest number of repetitions you are guaranteed is allowed in the

construct @samp{\@{@var{min},@var{max}\@}} in a regular expression.

The value of this macro is actually a lower bound for the maximum.  That

is, you can count on being able to have that many repetitions, but a

particular machine might let you have even more.  You can use

@code{sysconf} to see whether a particular machine will let you have

more (@pxref{Sysconf}).  And even the value that @code{sysconf} tells

you is just a lower bound---larger values might work.

This macro is defined in all POSIX.2 systems, because POSIX.2 says it

should always be defined even if there is no specific imposed limit.

@end deftypevr

@node System Options

@section Overall System Options

@cindex POSIX optional features

@cindex optional POSIX features

POSIX defines certain system-specific options that not all POSIX systems

support.  Since these options are provided in the kernel, not in the

library, simply using @theglibc{} does not guarantee any of these

features are supported; it depends on the system you are using.

@pindex unistd.h

You can test for the availability of a given option using the macros in

this section, together with the function @code{sysconf}.  The macros are

defined only if you include @file{unistd.h}.

For the following macros, if the macro is defined in @file{unistd.h},

then the option is supported.  Otherwise, the option may or may not be

supported; use @code{sysconf} to find out.  @xref{Sysconf}.

@deftypevr Macro int _POSIX_JOB_CONTROL

@standards{POSIX.1, unistd.h}

If this symbol is defined, it indicates that the system supports job

control.  Otherwise, the implementation behaves as if all processes

within a session belong to a single process group.  @xref{Job Control}.

@end deftypevr

@deftypevr Macro int _POSIX_SAVED_IDS

@standards{POSIX.1, unistd.h}

If this symbol is defined, it indicates that the system remembers the

effective user and group IDs of a process before it executes an

executable file with the set-user-ID or set-group-ID bits set, and that

explicitly changing the effective user or group IDs back to these values

is permitted.  If this option is not defined, then if a nonprivileged

process changes its effective user or group ID to the real user or group

ID of the process, it can't change it back again.  @xref{Enable/Disable

Setuid}.

@end deftypevr

For the following macros, if the macro is defined in @file{unistd.h},

then its value indicates whether the option is supported.  A value of

@code{-1} means no, and any other value means yes.  If the macro is not

defined, then the option may or may not be supported; use @code{sysconf}

to find out.  @xref{Sysconf}.

@deftypevr Macro int _POSIX2_C_DEV

@standards{POSIX.2, unistd.h}

If this symbol is defined, it indicates that the system has the POSIX.2

C compiler command, @code{c89}.  @Theglibc{} always defines this

as @code{1}, on the assumption that you would not have installed it if

you didn't have a C compiler.

@end deftypevr

@deftypevr Macro int _POSIX2_FORT_DEV

@standards{POSIX.2, unistd.h}

If this symbol is defined, it indicates that the system has the POSIX.2

Fortran compiler command, @code{fort77}.  @Theglibc{} never

defines this, because we don't know what the system has.

@end deftypevr

@deftypevr Macro int _POSIX2_FORT_RUN

@standards{POSIX.2, unistd.h}

If this symbol is defined, it indicates that the system has the POSIX.2

@code{asa} command to interpret Fortran carriage control.  @Theglibc{}

never defines this, because we don't know what the system has.

@end deftypevr

@deftypevr Macro int _POSIX2_LOCALEDEF

@standards{POSIX.2, unistd.h}

If this symbol is defined, it indicates that the system has the POSIX.2

@code{localedef} command.  @Theglibc{} never defines this, because

we don't know what the system has.

@end deftypevr

@deftypevr Macro int _POSIX2_SW_DEV

@standards{POSIX.2, unistd.h}

If this symbol is defined, it indicates that the system has the POSIX.2

commands @code{ar}, @code{make}, and @code{strip}.  @Theglibc{}

always defines this as @code{1}, on the assumption that you had to have

@code{ar} and @code{make} to install the library, and it's unlikely that

@code{strip} would be absent when those are present.

@end deftypevr

@node Version Supported

@section Which Version of POSIX is Supported

@deftypevr Macro {long int} _POSIX_VERSION

@standards{POSIX.1, unistd.h}

This constant represents the version of the POSIX.1 standard to which

the implementation conforms.  For an implementation conforming to the

1995 POSIX.1 standard, the value is the integer @code{199506L}.

@code{_POSIX_VERSION} is always defined (in @file{unistd.h}) in any

POSIX system.

@strong{Usage Note:} Don't try to test whether the system supports POSIX

by including @file{unistd.h} and then checking whether

@code{_POSIX_VERSION} is defined.  On a non-POSIX system, this will

probably fail because there is no @file{unistd.h}.  We do not know of

@emph{any} way you can reliably test at compilation time whether your

target system supports POSIX or whether @file{unistd.h} exists.

@end deftypevr

@deftypevr Macro {long int} _POSIX2_C_VERSION

@standards{POSIX.2, unistd.h}

This constant represents the version of the POSIX.2 standard which the

library and system kernel support.  We don't know what value this will

be for the first version of the POSIX.2 standard, because the value is

based on the year and month in which the standard is officially adopted.

The value of this symbol says nothing about the utilities installed on

the system.

@strong{Usage Note:} You can use this macro to tell whether a POSIX.1

system library supports POSIX.2 as well.  Any POSIX.1 system contains

@file{unistd.h}, so include that file and then test @code{defined

(_POSIX2_C_VERSION)}.

@end deftypevr

@node Sysconf

@section Using @code{sysconf}

When your system has configurable system limits, you can use the

@code{sysconf} function to find out the value that applies to any

particular machine.  The function and the associated @var{parameter}

constants are declared in the header file @file{unistd.h}.

@menu

* Sysconf Definition::        Detailed specifications of @code{sysconf}.

* Constants for Sysconf::     The list of parameters @code{sysconf} can read.

* Examples of Sysconf::       How to use @code{sysconf} and the parameter

				 macros properly together.

@end menu

@node Sysconf Definition

@subsection Definition of @code{sysconf}

@deftypefun {long int} sysconf (int @var{parameter})

@standards{POSIX.1, unistd.h}

@safety{@prelim{}@mtsafe{@mtsenv{}}@asunsafe{@asulock{} @ascuheap{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}}

@c Some parts of the implementation open /proc and /sys files and dirs

@c to collect system details, using fd and stream I/O depending on the

@c case.  The returned max value may change over time for NPROCS,

@c NPROCS_CONF, PHYS_PAGES, AVPHYS_PAGES, NGROUPS_MAX, SIGQUEUE_MAX,

@c depending on variable values read from /proc at each call, and from

@c rlimit-obtained values CHILD_MAX, OPEN_MAX, ARG_MAX, SIGQUEUE_MAX.

This function is used to inquire about runtime system parameters.  The

@var{parameter} argument should be one of the @samp{_SC_} symbols listed

below.

The normal return value from @code{sysconf} is the value you requested.

A value of @code{-1} is returned both if the implementation does not

impose a limit, and in case of an error.

The following @code{errno} error conditions are defined for this function:

@table @code

@item EINVAL

The value of the @var{parameter} is invalid.

@end table

@end deftypefun

@node Constants for Sysconf

@subsection Constants for @code{sysconf} Parameters

Here are the symbolic constants for use as the @var{parameter} argument

to @code{sysconf}.  The values are all integer constants (more

specifically, enumeration type values).

@vtable @code

@item _SC_ARG_MAX

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to @code{ARG_MAX}.

@item _SC_CHILD_MAX

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to @code{CHILD_MAX}.

@item _SC_OPEN_MAX

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to @code{OPEN_MAX}.

@item _SC_STREAM_MAX

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to @code{STREAM_MAX}.

@item _SC_TZNAME_MAX

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to @code{TZNAME_MAX}.

@item _SC_NGROUPS_MAX

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to @code{NGROUPS_MAX}.

@item _SC_JOB_CONTROL

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_JOB_CONTROL}.

@item _SC_SAVED_IDS

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_SAVED_IDS}.

@item _SC_VERSION

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_VERSION}.

@item _SC_CLK_TCK

@standards{POSIX.1, unistd.h}

Inquire about the number of clock ticks per second; @pxref{CPU Time}.

The corresponding parameter @code{CLK_TCK} is obsolete.

@item _SC_CHARCLASS_NAME_MAX

@standards{GNU, unistd.h}

Inquire about the parameter corresponding to maximal length allowed for

a character class name in an extended locale specification.  These

extensions are not yet standardized and so this option is not standardized

as well.

@item _SC_REALTIME_SIGNALS

@standards{POSIX.1, unistdh.h}

Inquire about the parameter corresponding to @code{_POSIX_REALTIME_SIGNALS}.

@item _SC_PRIORITY_SCHEDULING

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_PRIORITY_SCHEDULING}.

@item _SC_TIMERS

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_TIMERS}.

@item _SC_ASYNCHRONOUS_IO

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_ASYNCHRONOUS_IO}.

@item _SC_PRIORITIZED_IO

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_PRIORITIZED_IO}.

@item _SC_SYNCHRONIZED_IO

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_SYNCHRONIZED_IO}.

@item _SC_FSYNC

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_FSYNC}.

@item _SC_MAPPED_FILES

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_MAPPED_FILES}.

@item _SC_MEMLOCK

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_MEMLOCK}.

@item _SC_MEMLOCK_RANGE

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_MEMLOCK_RANGE}.

@item _SC_MEMORY_PROTECTION

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_MEMORY_PROTECTION}.

@item _SC_MESSAGE_PASSING

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_MESSAGE_PASSING}.

@item _SC_SEMAPHORES

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_SEMAPHORES}.

@item _SC_SHARED_MEMORY_OBJECTS

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to@*

@code{_POSIX_SHARED_MEMORY_OBJECTS}.

@item _SC_AIO_LISTIO_MAX

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_AIO_LISTIO_MAX}.

@item _SC_AIO_MAX

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_AIO_MAX}.

@item _SC_AIO_PRIO_DELTA_MAX

@standards{POSIX.1, unistd.h}

Inquire about the value by which a process can decrease its asynchronous I/O

priority level from its own scheduling priority.  This corresponds to the

run-time invariant value @code{AIO_PRIO_DELTA_MAX}.

@item _SC_DELAYTIMER_MAX

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_DELAYTIMER_MAX}.

@item _SC_MQ_OPEN_MAX

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_MQ_OPEN_MAX}.

@item _SC_MQ_PRIO_MAX

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_MQ_PRIO_MAX}.

@item _SC_RTSIG_MAX

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_RTSIG_MAX}.

@item _SC_SEM_NSEMS_MAX

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_SEM_NSEMS_MAX}.

@item _SC_SEM_VALUE_MAX

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_SEM_VALUE_MAX}.

@item _SC_SIGQUEUE_MAX

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_SIGQUEUE_MAX}.

@item _SC_TIMER_MAX

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_TIMER_MAX}.

@item _SC_PII

@standards{POSIX.1g, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_PII}.

@item _SC_PII_XTI

@standards{POSIX.1g, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_PII_XTI}.

@item _SC_PII_SOCKET

@standards{POSIX.1g, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_PII_SOCKET}.

@item _SC_PII_INTERNET

@standards{POSIX.1g, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_PII_INTERNET}.

@item _SC_PII_OSI

@standards{POSIX.1g, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_PII_OSI}.

@item _SC_SELECT

@standards{POSIX.1g, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_SELECT}.

@item _SC_UIO_MAXIOV

@standards{POSIX.1g, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_UIO_MAXIOV}.

@item _SC_PII_INTERNET_STREAM

@standards{POSIX.1g, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_PII_INTERNET_STREAM}.

@item _SC_PII_INTERNET_DGRAM

@standards{POSIX.1g, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_PII_INTERNET_DGRAM}.

@item _SC_PII_OSI_COTS

@standards{POSIX.1g, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_PII_OSI_COTS}.

@item _SC_PII_OSI_CLTS

@standards{POSIX.1g, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_PII_OSI_CLTS}.

@item _SC_PII_OSI_M

@standards{POSIX.1g, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_PII_OSI_M}.

@item _SC_T_IOV_MAX

@standards{POSIX.1g, unistd.h}

Inquire about the value associated with the @code{T_IOV_MAX}

variable.

@item _SC_THREADS

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_THREADS}.

@item _SC_THREAD_SAFE_FUNCTIONS

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to@*

@code{_POSIX_THREAD_SAFE_FUNCTIONS}.

@item _SC_GETGR_R_SIZE_MAX

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_GETGR_R_SIZE_MAX}.

@item _SC_GETPW_R_SIZE_MAX

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_GETPW_R_SIZE_MAX}.

@item _SC_LOGIN_NAME_MAX

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_LOGIN_NAME_MAX}.

@item _SC_TTY_NAME_MAX

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_TTY_NAME_MAX}.

@item _SC_THREAD_DESTRUCTOR_ITERATIONS

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to

@code{_POSIX_THREAD_DESTRUCTOR_ITERATIONS}.

@item _SC_THREAD_KEYS_MAX

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_THREAD_KEYS_MAX}.

@item _SC_THREAD_STACK_MIN

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_THREAD_STACK_MIN}.

@item _SC_THREAD_THREADS_MAX

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_THREAD_THREADS_MAX}.

@item _SC_THREAD_ATTR_STACKADDR

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to@*a

@code{_POSIX_THREAD_ATTR_STACKADDR}.

@item _SC_THREAD_ATTR_STACKSIZE

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to@*

@code{_POSIX_THREAD_ATTR_STACKSIZE}.

@item _SC_THREAD_PRIORITY_SCHEDULING

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to

@code{_POSIX_THREAD_PRIORITY_SCHEDULING}.

@item _SC_THREAD_PRIO_INHERIT

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_THREAD_PRIO_INHERIT}.

@item _SC_THREAD_PRIO_PROTECT

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to @code{_POSIX_THREAD_PRIO_PROTECT}.

@item _SC_THREAD_PROCESS_SHARED

@standards{POSIX.1, unistd.h}

Inquire about the parameter corresponding to

@code{_POSIX_THREAD_PROCESS_SHARED}.

@item _SC_2_C_DEV

@standards{POSIX.2, unistd.h}

Inquire about whether the system has the POSIX.2 C compiler command,

@code{c89}.

@item _SC_2_FORT_DEV

@standards{POSIX.2, unistd.h}

Inquire about whether the system has the POSIX.2 Fortran compiler

command, @code{fort77}.

@item _SC_2_FORT_RUN

@standards{POSIX.2, unistd.h}

Inquire about whether the system has the POSIX.2 @code{asa} command to

interpret Fortran carriage control.

@item _SC_2_LOCALEDEF

@standards{POSIX.2, unistd.h}

Inquire about whether the system has the POSIX.2 @code{localedef}

command.

@item _SC_2_SW_DEV

@standards{POSIX.2, unistd.h}

Inquire about whether the system has the POSIX.2 commands @code{ar},

@code{make}, and @code{strip}.

@item _SC_BC_BASE_MAX

@standards{POSIX.2, unistd.h}

Inquire about the maximum value of @code{obase} in the @code{bc}

utility.

@item _SC_BC_DIM_MAX

@standards{POSIX.2, unistd.h}

Inquire about the maximum size of an array in the @code{bc}

utility.

@item _SC_BC_SCALE_MAX

@standards{POSIX.2, unistd.h}

Inquire about the maximum value of @code{scale} in the @code{bc}

utility.

@item _SC_BC_STRING_MAX

@standards{POSIX.2, unistd.h}

Inquire about the maximum size of a string constant in the

@code{bc} utility.

@item _SC_COLL_WEIGHTS_MAX

@standards{POSIX.2, unistd.h}

Inquire about the maximum number of weights that can necessarily

be used in defining the collating sequence for a locale.

@item _SC_EXPR_NEST_MAX

@standards{POSIX.2, unistd.h}

Inquire about the maximum number of expressions nested within

parentheses when using the @code{expr} utility.

@item _SC_LINE_MAX

@standards{POSIX.2, unistd.h}

Inquire about the maximum size of a text line that the POSIX.2 text

utilities can handle.

@item _SC_EQUIV_CLASS_MAX

@standards{POSIX.2, unistd.h}

Inquire about the maximum number of weights that can be assigned to an

entry of the @code{LC_COLLATE} category @samp{order} keyword in a locale

definition.  @Theglibc{} does not presently support locale

definitions.

@item _SC_VERSION

@standards{POSIX.2, unistd.h}

Inquire about the version number of POSIX.1 that the library and kernel

support.

@item _SC_2_VERSION

@standards{POSIX.2, unistd.h}

Inquire about the version number of POSIX.2 that the system utilities

support.

@item _SC_PAGESIZE

@standards{GNU, unistd.h}

Inquire about the virtual memory page size of the machine.

@code{getpagesize} returns the same value (@pxref{Query Memory Parameters}).

@item _SC_NPROCESSORS_CONF

@standards{GNU, unistd.h}

Inquire about the number of configured processors.

@item _SC_NPROCESSORS_ONLN

@standards{GNU, unistd.h}

Inquire about the number of processors online.

@item _SC_PHYS_PAGES

@standards{GNU, unistd.h}

Inquire about the number of physical pages in the system.

@item _SC_AVPHYS_PAGES

@standards{GNU, unistd.h}

Inquire about the number of available physical pages in the system.

@item _SC_ATEXIT_MAX

@standards{GNU, unistd.h}

Inquire about the number of functions which can be registered as termination

functions for @code{atexit}; @pxref{Cleanups on Exit}.

@item _SC_LEVEL1_ICACHE_SIZE

@standards{GNU, unistd.h}

Inquire about the size of the Level 1 instruction cache.

@item _SC_LEVEL1_ICACHE_ASSOC

@standards{GNU, unistd.h}

Inquire about the associativity of the Level 1 instruction cache.

@item _SC_LEVEL1_ICACHE_LINESIZE

@standards{GNU, unistd.h}

Inquire about the line length of the Level 1 instruction cache.

On aarch64, the cache line size returned is the minimum instruction cache line

size observable by userspace.  This is typically the same as the L1 icache

size but on some cores it may not be so.  However, it is specified in the

architecture that operations such as cache line invalidation are consistent

with the size reported with this variable.

@item _SC_LEVEL1_DCACHE_SIZE

@standards{GNU, unistd.h}

Inquire about the size of the Level 1 data cache.

@item _SC_LEVEL1_DCACHE_ASSOC

@standards{GNU, unistd.h}

Inquire about the associativity of the Level 1 data cache.

@item _SC_LEVEL1_DCACHE_LINESIZE

@standards{GNU, unistd.h}

Inquire about the line length of the Level 1 data cache.

On aarch64, the cache line size returned is the minimum data cache line size

observable by userspace.  This is typically the same as the L1 dcache size but

on some cores it may not be so.  However, it is specified in the architecture

that operations such as cache line invalidation are consistent with the size

reported with this variable.

@item _SC_LEVEL2_CACHE_SIZE

@standards{GNU, unistd.h}

Inquire about the size of the Level 2 cache.

@item _SC_LEVEL2_CACHE_ASSOC

@standards{GNU, unistd.h}

Inquire about the associativity of the Level 2 cache.

@item _SC_LEVEL2_CACHE_LINESIZE

@standards{GNU, unistd.h}

Inquire about the line length of the Level 2 cache.

@item _SC_LEVEL3_CACHE_SIZE

@standards{GNU, unistd.h}

Inquire about the size of the Level 3 cache.

@item _SC_LEVEL3_CACHE_ASSOC

@standards{GNU, unistd.h}

Inquire about the associativity of the Level 3 cache.

@item _SC_LEVEL3_CACHE_LINESIZE

@standards{GNU, unistd.h}

Inquire about the line length of the Level 3 cache.

@item _SC_LEVEL4_CACHE_SIZE

@standards{GNU, unistd.h}

Inquire about the size of the Level 4 cache.

@item _SC_LEVEL4_CACHE_ASSOC

@standards{GNU, unistd.h}

Inquire about the associativity of the Level 4 cache.

@item _SC_LEVEL4_CACHE_LINESIZE

@standards{GNU, unistd.h}

Inquire about the line length of the Level 4 cache.

@item _SC_XOPEN_VERSION

@standards{X/Open, unistd.h}

Inquire about the parameter corresponding to @code{_XOPEN_VERSION}.

@item _SC_XOPEN_XCU_VERSION

@standards{X/Open, unistd.h}

Inquire about the parameter corresponding to @code{_XOPEN_XCU_VERSION}.

@item _SC_XOPEN_UNIX

@standards{X/Open, unistd.h}

Inquire about the parameter corresponding to @code{_XOPEN_UNIX}.

@item _SC_XOPEN_REALTIME

@standards{X/Open, unistd.h}

Inquire about the parameter corresponding to @code{_XOPEN_REALTIME}.

@item _SC_XOPEN_REALTIME_THREADS

@standards{X/Open, unistd.h}

Inquire about the parameter corresponding to @code{_XOPEN_REALTIME_THREADS}.

@item _SC_XOPEN_LEGACY

@standards{X/Open, unistd.h}

Inquire about the parameter corresponding to @code{_XOPEN_LEGACY}.

@item _SC_XOPEN_CRYPT

@standards{X/Open, unistd.h}

Inquire about the parameter corresponding to @code{_XOPEN_CRYPT}.

@Theglibc no longer implements the @code{_XOPEN_CRYPT} extensions,

so @samp{sysconf (_SC_XOPEN_CRYPT)} always returns @code{-1}.

@item _SC_XOPEN_ENH_I18N

@standards{X/Open, unistd.h}

Inquire about the parameter corresponding to @code{_XOPEN_ENH_I18N}.

@item _SC_XOPEN_SHM

@standards{X/Open, unistd.h}

Inquire about the parameter corresponding to @code{_XOPEN_SHM}.

@item _SC_XOPEN_XPG2

@standards{X/Open, unistd.h}

Inquire about the parameter corresponding to @code{_XOPEN_XPG2}.

@item _SC_XOPEN_XPG3

@standards{X/Open, unistd.h}

Inquire about the parameter corresponding to @code{_XOPEN_XPG3}.

@item _SC_XOPEN_XPG4

@standards{X/Open, unistd.h}

Inquire about the parameter corresponding to @code{_XOPEN_XPG4}.

@item _SC_CHAR_BIT

@standards{X/Open, unistd.h}

Inquire about the number of bits in a variable of type @code{char}.

@item _SC_CHAR_MAX

@standards{X/Open, unistd.h}

Inquire about the maximum value which can be stored in a variable of type

@code{char}.

@item _SC_CHAR_MIN

@standards{X/Open, unistd.h}

Inquire about the minimum value which can be stored in a variable of type

@code{char}.

@item _SC_INT_MAX

@standards{X/Open, unistd.h}

Inquire about the maximum value which can be stored in a variable of type

@code{int}.

@item _SC_INT_MIN

@standards{X/Open, unistd.h}

Inquire about the minimum value which can be stored in a variable of type

@code{int}.

@item _SC_LONG_BIT

@standards{X/Open, unistd.h}

Inquire about the number of bits in a variable of type @code{long int}.

@item _SC_WORD_BIT

@standards{X/Open, unistd.h}

Inquire about the number of bits in a variable of a register word.

@item _SC_MB_LEN_MAX

@standards{X/Open, unistd.h}

Inquire about the maximum length of a multi-byte representation of a wide

character value.

@item _SC_NZERO

@standards{X/Open, unistd.h}

Inquire about the value used to internally represent the zero priority level for

the process execution.

@item _SC_SSIZE_MAX

@standards{X/Open, unistd.h}

Inquire about the maximum value which can be stored in a variable of type

@code{ssize_t}.

@item _SC_SCHAR_MAX

@standards{X/Open, unistd.h}

Inquire about the maximum value which can be stored in a variable of type

@code{signed char}.

@item _SC_SCHAR_MIN

@standards{X/Open, unistd.h}

Inquire about the minimum value which can be stored in a variable of type

@code{signed char}.

@item _SC_SHRT_MAX

@standards{X/Open, unistd.h}

Inquire about the maximum value which can be stored in a variable of type

@code{short int}.

@item _SC_SHRT_MIN

@standards{X/Open, unistd.h}

Inquire about the minimum value which can be stored in a variable of type

@code{short int}.

@item _SC_UCHAR_MAX

@standards{X/Open, unistd.h}

Inquire about the maximum value which can be stored in a variable of type

@code{unsigned char}.

@item _SC_UINT_MAX

@standards{X/Open, unistd.h}

Inquire about the maximum value which can be stored in a variable of type

@code{unsigned int}.