Originální popis anglicky:
sysconf - get configurable system variables
Návod, kniha: POSIX Programmer's Manual
#include <unistd.h>
long sysconf(int
name);
The
sysconf() function provides a method for the application to determine
the current value of a configurable system limit or option (
variable).
The implementation shall support all of the variables listed in the following
table and may support others.
The
name argument represents the system variable to be queried. The
following table lists the minimal set of system variables from
<limits.h> or
<unistd.h> that can be returned by
sysconf(), and the symbolic constants defined in
<unistd.h> that are the corresponding values used for
name.
| Variable |
Value of Name |
| {AIO_LISTIO_MAX} |
_SC_AIO_LISTIO_MAX |
| {AIO_MAX} |
_SC_AIO_MAX |
| {AIO_PRIO_DELTA_MAX} |
_SC_AIO_PRIO_DELTA_MAX |
| {ARG_MAX} |
_SC_ARG_MAX |
| {ATEXIT_MAX} |
_SC_ATEXIT_MAX |
| {BC_BASE_MAX} |
_SC_BC_BASE_MAX |
| {BC_DIM_MAX} |
_SC_BC_DIM_MAX |
| {BC_SCALE_MAX} |
_SC_BC_SCALE_MAX |
| {BC_STRING_MAX} |
_SC_BC_STRING_MAX |
| {CHILD_MAX} |
_SC_CHILD_MAX |
| Clock ticks/second |
_SC_CLK_TCK |
| {COLL_WEIGHTS_MAX} |
_SC_COLL_WEIGHTS_MAX |
| {DELAYTIMER_MAX} |
_SC_DELAYTIMER_MAX |
| {EXPR_NEST_MAX} |
_SC_EXPR_NEST_MAX |
| {HOST_NAME_MAX} |
_SC_HOST_NAME_MAX |
| {IOV_MAX} |
_SC_IOV_MAX |
| {LINE_MAX} |
_SC_LINE_MAX |
| {LOGIN_NAME_MAX} |
_SC_LOGIN_NAME_MAX |
| {NGROUPS_MAX} |
_SC_NGROUPS_MAX |
| Maximum size of getgrgid_r() and |
_SC_GETGR_R_SIZE_MAX |
| getgrnam_r() data buffers |
|
| Maximum size of getpwuid_r() and |
_SC_GETPW_R_SIZE_MAX |
| getpwnam_r() data buffers |
|
| {MQ_OPEN_MAX} |
_SC_MQ_OPEN_MAX |
| {MQ_PRIO_MAX} |
_SC_MQ_PRIO_MAX |
| {OPEN_MAX} |
_SC_OPEN_MAX |
| _POSIX_ADVISORY_INFO |
_SC_ADVISORY_INFO |
| _POSIX_BARRIERS |
_SC_BARRIERS |
| _POSIX_ASYNCHRONOUS_IO |
_SC_ASYNCHRONOUS_IO |
| _POSIX_CLOCK_SELECTION |
_SC_CLOCK_SELECTION |
| _POSIX_CPUTIME |
_SC_CPUTIME |
| _POSIX_FILE_LOCKING |
_SC_FILE_LOCKING |
| _POSIX_FSYNC |
_SC_FSYNC |
| _POSIX_IPV6 |
_SC_IPV6 |
| _POSIX_JOB_CONTROL |
_SC_JOB_CONTROL |
| _POSIX_MAPPED_FILES |
_SC_MAPPED_FILES |
| _POSIX_MEMLOCK |
_SC_MEMLOCK |
| _POSIX_MEMLOCK_RANGE |
_SC_MEMLOCK_RANGE |
| _POSIX_MEMORY_PROTECTION |
_SC_MEMORY_PROTECTION |
| _POSIX_MESSAGE_PASSING |
_SC_MESSAGE_PASSING |
| _POSIX_MONOTONIC_CLOCK |
_SC_MONOTONIC_CLOCK |
| _POSIX_MULTI_PROCESS |
_SC_MULTI_PROCESS |
| _POSIX_PRIORITIZED_IO |
_SC_PRIORITIZED_IO |
| _POSIX_PRIORITY_SCHEDULING |
_SC_PRIORITY_SCHEDULING |
| _POSIX_RAW_SOCKETS |
_SC_RAW_SOCKETS |
| _POSIX_READER_WRITER_LOCKS |
_SC_READER_WRITER_LOCKS |
| _POSIX_REALTIME_SIGNALS |
_SC_REALTIME_SIGNALS |
| _POSIX_REGEXP |
_SC_REGEXP |
| _POSIX_SAVED_IDS |
_SC_SAVED_IDS |
| _POSIX_SEMAPHORES |
_SC_SEMAPHORES |
| _POSIX_SHARED_MEMORY_OBJECTS |
_SC_SHARED_MEMORY_OBJECTS |
| _POSIX_SHELL |
_SC_SHELL |
| _POSIX_SPAWN |
_SC_SPAWN |
| _POSIX_SPIN_LOCKS |
_SC_SPIN_LOCKS |
| _POSIX_SPORADIC_SERVER |
_SC_SPORADIC_SERVER |
| _POSIX_SYMLOOP_MAX |
_SC_SYMLOOP_MAX |
| _POSIX_SYNCHRONIZED_IO |
_SC_SYNCHRONIZED_IO |
| _POSIX_THREAD_ATTR_STACKADDR |
_SC_THREAD_ATTR_STACKADDR |
| _POSIX_THREAD_ATTR_STACKSIZE |
_SC_THREAD_ATTR_STACKSIZE |
| _POSIX_THREAD_CPUTIME |
_SC_THREAD_CPUTIME |
| _POSIX_THREAD_PRIO_INHERIT |
_SC_THREAD_PRIO_INHERIT |
| _POSIX_THREAD_PRIO_PROTECT |
_SC_THREAD_PRIO_PROTECT |
| _POSIX_THREAD_PRIORITY_SCHEDULING |
_SC_THREAD_PRIORITY_SCHEDULING |
| _POSIX_THREAD_PROCESS_SHARED |
_SC_THREAD_PROCESS_SHARED |
| _POSIX_THREAD_SAFE_FUNCTIONS |
_SC_THREAD_SAFE_FUNCTIONS |
| _POSIX_THREAD_SPORADIC_SERVER |
_SC_THREAD_SPORADIC_SERVER |
| _POSIX_THREADS |
_SC_THREADS |
| _POSIX_TIMEOUTS |
_SC_TIMEOUTS |
| _POSIX_TIMERS |
_SC_TIMERS |
| _POSIX_TRACE |
_SC_TRACE |
| _POSIX_TRACE_EVENT_FILTER |
_SC_TRACE_EVENT_FILTER |
| _POSIX_TRACE_INHERIT |
_SC_TRACE_INHERIT |
| _POSIX_TRACE_LOG |
_SC_TRACE_LOG |
| _POSIX_TYPED_MEMORY_OBJECTS |
_SC_TYPED_MEMORY_OBJECTS |
| _POSIX_VERSION |
_SC_VERSION |
| _POSIX_V6_ILP32_OFF32 |
_SC_V6_ILP32_OFF32 |
| _POSIX_V6_ILP32_OFFBIG |
_SC_V6_ILP32_OFFBIG |
| _POSIX_V6_LP64_OFF64 |
_SC_V6_LP64_OFF64 |
| _POSIX_V6_LPBIG_OFFBIG |
_SC_V6_LPBIG_OFFBIG |
| _POSIX2_C_BIND |
_SC_2_C_BIND |
| _POSIX2_C_DEV |
_SC_2_C_DEV |
| _POSIX2_C_VERSION |
_SC_2_C_VERSION |
| _POSIX2_CHAR_TERM |
_SC_2_CHAR_TERM |
| _POSIX2_FORT_DEV |
_SC_2_FORT_DEV |
| _POSIX2_FORT_RUN |
_SC_2_FORT_RUN |
| _POSIX2_LOCALEDEF |
_SC_2_LOCALEDEF |
| _POSIX2_PBS |
_SC_2_PBS |
| _POSIX2_PBS_ACCOUNTING |
_SC_2_PBS_ACCOUNTING |
| _POSIX2_PBS_CHECKPOINT |
_SC_2_PBS_CHECKPOINT |
| _POSIX2_PBS_LOCATE |
_SC_2_PBS_LOCATE |
| _POSIX2_PBS_MESSAGE |
_SC_2_PBS_MESSAGE |
| _POSIX2_PBS_TRACK |
_SC_2_PBS_TRACK |
| _POSIX2_SW_DEV |
_SC_2_SW_DEV |
| _POSIX2_UPE |
_SC_2_UPE |
| _POSIX2_VERSION |
_SC_2_VERSION |
| _REGEX_VERSION |
_SC_REGEX_VERSION |
| {PAGE_SIZE} |
_SC_PAGE_SIZE |
| {PAGESIZE} |
_SC_PAGESIZE |
| {PTHREAD_DESTRUCTOR_ITERATIONS} |
_SC_THREAD_DESTRUCTOR_ITERATIONS |
| {PTHREAD_KEYS_MAX} |
_SC_THREAD_KEYS_MAX |
| {PTHREAD_STACK_MIN} |
_SC_THREAD_STACK_MIN |
| {PTHREAD_THREADS_MAX} |
_SC_THREAD_THREADS_MAX |
| {RE_DUP_MAX} |
_SC_RE_DUP_MAX |
| {RTSIG_MAX} |
_SC_RTSIG_MAX |
| {SEM_NSEMS_MAX} |
_SC_SEM_NSEMS_MAX |
| {SEM_VALUE_MAX} |
_SC_SEM_VALUE_MAX |
| {SIGQUEUE_MAX} |
_SC_SIGQUEUE_MAX |
| {STREAM_MAX} |
_SC_STREAM_MAX |
| {SYMLOOP_MAX} |
_SC_SYMLOOP_MAX |
| {TIMER_MAX} |
_SC_TIMER_MAX |
| {TTY_NAME_MAX} |
_SC_TTY_NAME_MAX |
| {TZNAME_MAX} |
_SC_TZNAME_MAX |
| _XBS5_ILP32_OFF32 (LEGACY) |
_SC_XBS5_ILP32_OFF32 (LEGACY) |
| _XBS5_ILP32_OFFBIG (LEGACY) |
_SC_XBS5_ILP32_OFFBIG (LEGACY) |
| _XBS5_LP64_OFF64 (LEGACY) |
_SC_XBS5_LP64_OFF64 (LEGACY) |
| _XBS5_LPBIG_OFFBIG (LEGACY) |
_SC_XBS5_LPBIG_OFFBIG (LEGACY) |
| _XOPEN_CRYPT |
_SC_XOPEN_CRYPT |
| _XOPEN_ENH_I18N |
_SC_XOPEN_ENH_I18N |
| _XOPEN_LEGACY |
_SC_XOPEN_LEGACY |
| _XOPEN_REALTIME |
_SC_XOPEN_REALTIME |
| _XOPEN_REALTIME_THREADS |
_SC_XOPEN_REALTIME_THREADS |
| _XOPEN_SHM |
_SC_XOPEN_SHM |
| _XOPEN_STREAMS |
_SC_XOPEN_STREAMS |
| _XOPEN_UNIX |
_SC_XOPEN_UNIX |
| _XOPEN_VERSION |
_SC_XOPEN_VERSION |
| _XOPEN_XCU_VERSION |
_SC_XOPEN_XCU_VERSION |
If
name is an invalid value,
sysconf() shall return -1 and set
errno to indicate the error. If the variable corresponding to
name has no limit,
sysconf() shall return -1 without changing
the value of
errno. Note that indefinite limits do not imply infinite
limits; see
<limits.h>.
Otherwise,
sysconf() shall return the current variable value on the
system. The value returned shall not be more restrictive than the
corresponding value described to the application when it was compiled with the
implementation's
<limits.h> or
<unistd.h>. The value
shall not change during the lifetime of the calling process, except
that
sysconf(_SC_OPEN_MAX) may return different values before and after
a call to
setrlimit() which changes the RLIMIT_NOFILE soft limit.
The
sysconf() function shall fail if:
- EINVAL
- The value of the name argument is invalid.
The following sections are informative.
None.
As -1 is a permissible return value in a successful situation, an application
wishing to check for error situations should set
errno to 0, then call
sysconf(), and, if it returns -1, check to see if
errno is
non-zero.
If the value of
sysconf(_SC_2_VERSION) is not equal to the value of the
_POSIX2_VERSION symbolic constant, the utilities available via
system()
or
popen() might not behave as described in the Shell and Utilities
volume of IEEE Std 1003.1-2001. This would mean that the
application is not running in an environment that conforms to the Shell and
Utilities volume of IEEE Std 1003.1-2001. Some applications
might be able to deal with this, others might not. However, the functions
defined in this volume of IEEE Std 1003.1-2001 continue to
operate as specified, even if
sysconf(_SC_2_VERSION) reports that the
utilities no longer perform as specified.
This functionality was added in response to requirements of application
developers and of system vendors who deal with many international system
configurations. It is closely related to
pathconf() and
fpathconf().
Although a conforming application can run on all systems by never demanding more
resources than the minimum values published in this volume of
IEEE Std 1003.1-2001, it is useful for that application to be
able to use the actual value for the quantity of a resource available on any
given system. To do this, the application makes use of the value of a symbolic
constant in
<limits.h> or
<unistd.h>.
However, once compiled, the application must still be able to cope if the amount
of resource available is increased. To that end, an application may need a
means of determining the quantity of a resource, or the presence of an option,
at execution time.
Two examples are offered:
- 1.
- Applications may wish to act differently on systems with or
without job control. Applications vendors who wish to distribute only a
single binary package to all instances of a computer architecture would be
forced to assume job control is never available if it were to rely solely
on the <unistd.h> value published in this volume of
IEEE Std 1003.1-2001.
- 2.
- International applications vendors occasionally require
knowledge of the number of clock ticks per second. Without these
facilities, they would be required to either distribute their applications
partially in source form or to have 50 Hz and 60 Hz versions for the
various countries in which they operate.
It is the knowledge that many applications are actually distributed widely in
executable form that leads to this facility. If limited to the most
restrictive values in the headers, such applications would have to be prepared
to accept the most limited environments offered by the smallest
microcomputers. Although this is entirely portable, there was a consensus that
they should be able to take advantage of the facilities offered by large
systems, without the restrictions associated with source and object
distributions.
During the discussions of this feature, it was pointed out that it is almost
always possible for an application to discern what a value might be at runtime
by suitably testing the various functions themselves. And, in any event, it
could always be written to adequately deal with error returns from the various
functions. In the end, it was felt that this imposed an unreasonable level of
complication and sophistication on the application writer.
This runtime facility is not meant to provide ever-changing values that
applications have to check multiple times. The values are seen as changing no
more frequently than once per system initialization, such as by a system
administrator or operator with an automatic configuration program. This volume
of IEEE Std 1003.1-2001 specifies that they shall not change
within the lifetime of the process.
Some values apply to the system overall and others vary at the file system or
directory level. The latter are described in
pathconf() .
Note that all values returned must be expressible as integers. String values
were considered, but the additional flexibility of this approach was rejected
due to its added complexity of implementation and use.
Some values, such as {PATH_MAX}, are sometimes so large that they must not be
used to, say, allocate arrays. The
sysconf() function returns a
negative value to show that this symbolic constant is not even defined in this
case.
Similar to
pathconf(), this permits the implementation not to have a
limit. When one resource is infinite, returning an error indicating that some
other resource limit has been reached is conforming behavior.
None.
confstr() ,
pathconf() , the Base Definitions volume of
IEEE Std 1003.1-2001,
<limits.h>,
<unistd.h>, the Shell and Utilities volume of
IEEE Std 1003.1-2001,
getconf
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html
.
