NAME

sysconf − get configurable system variables

SYNOPSIS

#include <unistd.h>

long sysconf(int name);

MT-LEVEL

Safe

DESCRIPTION

The sysconf() function provides a method for an application to determine the current value of a configurable system limit or option (variable). 

The name argument represents the system variable to be queried.  The following table lists the minimal set of system variables from <limits.h> and <unistd.h> that can be returned by sysconf(), and the symbolic constants, defined in <unistd.h> that are the corresponding values used for name. 

_SC_ARG_MAXARG_MAXMax combined size
of argv[] and
envp[]
_SC_CHILD_MAXCHILD_MAXMax processes
allowed to any UID
_SC_CLK_TCKCLK_TCKTicks per second
(clock_t)
_SC_NGROUPS_MAXNGROUPS_MAXMax simultaneous
groups one process
may belong to
_SC_OPEN_MAXOPEN_MAXMax open files
per process
_SC_PASS_MAXPASS_MAX
_SC_PAGESIZEPAGESIZESystem memory
page size
_SC_JOB_CONTROL_POSIX_JOB_CONTROLJob control
supported (boolean)
_SC_SAVED_IDS_POSIX_SAVED_IDSSaved ids
(seteuid(2))
supported (boolean)
_SC_VERSION_POSIX_VERSIONVersion of the
POSIX.1 standard
supported
_SC_XOPEN_VERSION_XOPEN_VERSION
_SC_LOGNAME_MAXLOGNAME_MAX
_SC_NPROCESSORS_CONFNumber of
processors (CPUs)
configured
_SC_NPROCESSORS_ONLNNumber of
processors online
_SC_PHYS_PAGESThe total number
of pages of
physical memory
in the system.
_SC_AVPHYS_PAGESThe number of
pages of physical
memory not
currently in use
by the system.
_SC_AIO_LISTIO_MAXAIO_LISTIO_MAXMaximum number
of I/O operations
in a single list I/O
call supported by
the implementation.
_SC_AIO_MAXAIO_MAXMaximum number
of outstanding
asynchronous
I/O operations
supported by the
implementation.
_SC_AIO_PRIO_DELTA_MAXAIO_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_MAXDELAYTIMER_MAXMaximum number
of timer expiration
overruns.
_SC_MQ_OPEN_MAXMQ_OPEN_MAXThe maximum
number of open
message queue
descriptors a
process may hold.
_SC_MQ_PRIO_MAXMQ_PRIO_MAXThe maximum
number of message
priorities
supported by the
implementation.
_SC_RTSIG_MAXRTSIG_MAXMaximum number
of realtime
signals reserved
for application
use in this
implementation.
_SC_SEM_NSEMS_MAXSEM_NSEMS_MAXMaximum number
of semaphores that
a process may have.
_SC_SEM_VALUE_MAXSEM_VALUE_MAXThe maximum
value a semaphore
may have.
_SC_SIGQUEUE_MAXSIGQUEUE_MAXMaximum number
of queued signals
that a process may
send and have
pending at the
receiver(s) at
any time.
_SC_TIMER_MAXTIMER_MAXMaximum number
of timers per
process supported
by the
implementation.
_SC_ASYNCHRONOUS_IO_POSIX_ASYNCHRONOUS_IOSupports
Asynchronous
Input and Output.
_SC_FSYNC_POSIX_FSYNCSupports File
Synchronization.
_SC_MAPPED_FILES_POSIX_MAPPED_FILESSupports Memory
Mapped Files.
_SC_MEMLOCK_POSIX_MEMLOCKSupports Process
Memory Locking.
_SC_MEMLOCK_RANGE_POSIX_MEMLOCK_RANGESupports Range
Memory Locking.
_SC_MEMORY_PROTECTION_POSIX_MEMORY_PROTECTION Supports Memory
Protection.
_SC_MESSAGE_PASSING_POSIX_MESSAGE_PASSINGSupports Message
Passing.
_SC_PRIORITIZED_IO_POSIX_PRIORITIZED_IOSupports Prioritized
Input and Output.
_SC_PRIORITY_SCHEDULING_POSIX_PRIORITY_SCHEDULING Supports Process
Scheduling
_SC_REALTIME_SIGNALS_POSIX_REALTIME_SIGNALSSupports Realtime
Signals Extension.
_SC_SEMAPHORES_POSIX_SEMAPHORESSupports
Semaphores.
_SC_SHARED_MEMORY_OBJECTS_POSIX_SHARED_MEMORY_OBJECTS Supports Shared
Memory Objects.
_SC_SYNCHRONIZED_IO_POSIX_SYNCHRONIZED_IOSupports
Synchronized
Input and Output.
_SC_TIMERS_POSIX_TIMERSSupports Timers.

RETURN VALUES

If name is an invalid value, sysconf() will return −1 and set errno to indicate the error.  If sysconf() fails due to a value of name that is not defined on the system, the function will return a value of −1 without changing the value of errno. 

SEE ALSO

fpathconf(2), seteuid(2), setrlimit(2)

NOTES

A call to setrlimit() may cause the value of OPEN_MAX to change. 

Multiplying sysconf(_SC_PHYS_PAGES) or sysconf(_SC_AVPHYS_PAGES) by sysconf(_SC_PAGESIZE) to determine memory amount in bytes can exceed the maximum values representable in a long or unsigned long. 

_SC_PHYS_PAGES and _SC_AVPHYS_PAGES are specific to Solaris 2.3 and later releases. 

The value of CLK_TCK may be variable and it should not be assumed that CLK_TCK is a compile-time constant. 

SunOS 5.4  —  Last change: 22 Jan 1993