limits.h(0P) POSIX Programmer's Manual limits.h(0P)
PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the corresponding
Linux manual page for details of Linux behavior), or the interface may
not be implemented on Linux.
NAME
limits.h -- implementation-defined constants
SYNOPSIS
#include <limits.h>
DESCRIPTION
Some of the functionality described on this reference page extends the
ISO C standard. Applications shall define the appropriate feature test
macro (see the System Interfaces volume of POSIX.1-2008, Section 2.2,
The Compilation Environment) to enable the visibility of these symbols
in this header.
Many of the symbols listed here are not defined by the
ISO/IEC 9899:1999 standard. Such symbols are not shown as CX shaded,
except under the heading ``Numerical Limits''.
The <limits.h> header shall define macros and symbolic constants for
various limits. Different categories of limits are described below,
representing various limits on resources that the implementation
imposes on applications. All macros and symbolic constants defined in
this header shall be suitable for use in #if preprocessing directives.
Implementations may choose any appropriate value for each limit, pro-
vided it is not more restrictive than the Minimum Acceptable Values
listed below. Symbolic constant names beginning with _POSIX may be
found in <unistd.h>.
Applications should not assume any particular value for a limit. To
achieve maximum portability, an application should not require more
resource than the Minimum Acceptable Value quantity. However, an appli-
cation wishing to avail itself of the full amount of a resource avail-
able on an implementation may make use of the value given in <limits.h>
on that particular implementation, by using the macros and symbolic
constants listed below. It should be noted, however, that many of the
listed limits are not invariant, and at runtime, the value of the limit
may differ from those given in this header, for the following reasons:
* The limit is pathname-dependent.
* The limit differs between the compile and runtime machines.
For these reasons, an application may use the fpathconf(), pathconf(),
and sysconf() functions to determine the actual value of a limit at
runtime.
The items in the list ending in _MIN give the most negative values that
the mathematical types are guaranteed to be capable of representing.
Numbers of a more negative value may be supported on some implementa-
tions, as indicated by the <limits.h> header on the implementation, but
applications requiring such numbers are not guaranteed to be portable
to all implementations. For positive constants ending in _MIN, this
indicates the minimum acceptable value.
Runtime Invariant Values (Possibly Indeterminate)
A definition of one of the symbolic constants in the following list
shall be omitted from <limits.h> on specific implementations where the
corresponding value is equal to or greater than the stated minimum, but
is unspecified.
This indetermination might depend on the amount of available memory
space on a specific instance of a specific implementation. The actual
value supported by a specific instance shall be provided by the
sysconf() function.
{AIO_LISTIO_MAX}
Maximum number of I/O operations in a single list I/O call sup-
ported by the implementation.
Minimum Acceptable Value: {_POSIX_AIO_LISTIO_MAX}
{AIO_MAX}
Maximum number of outstanding asynchronous I/O operations sup-
ported by the implementation.
Minimum Acceptable Value: {_POSIX_AIO_MAX}
{AIO_PRIO_DELTA_MAX}
The maximum amount by which a process can decrease its asynchro-
nous I/O priority level from its own scheduling priority.
Minimum Acceptable Value: 0
{ARG_MAX}
Maximum length of argument to the exec functions including envi-
ronment data.
Minimum Acceptable Value: {_POSIX_ARG_MAX}
{ATEXIT_MAX}
Maximum number of functions that may be registered with atexit().
Minimum Acceptable Value: 32
{CHILD_MAX}
Maximum number of simultaneous processes per real user ID.
Minimum Acceptable Value: {_POSIX_CHILD_MAX}
{DELAYTIMER_MAX}
Maximum number of timer expiration overruns.
Minimum Acceptable Value: {_POSIX_DELAYTIMER_MAX}
{HOST_NAME_MAX}
Maximum length of a host name (not including the terminating
null) as returned from the gethostname() function.
Minimum Acceptable Value: {_POSIX_HOST_NAME_MAX}
{IOV_MAX}
Maximum number of iovec structures that one process has available
for use with readv() or writev().
Minimum Acceptable Value: {_XOPEN_IOV_MAX}
{LOGIN_NAME_MAX}
Maximum length of a login name.
Minimum Acceptable Value: {_POSIX_LOGIN_NAME_MAX}
{MQ_OPEN_MAX}
The maximum number of open message queue descriptors a process
may hold.
Minimum Acceptable Value: {_POSIX_MQ_OPEN_MAX}
{MQ_PRIO_MAX}
The maximum number of message priorities supported by the imple-
mentation.
Minimum Acceptable Value: {_POSIX_MQ_PRIO_MAX}
{OPEN_MAX}
A value one greater than the maximum value that the system may
assign to a newly-created file descriptor.
Minimum Acceptable Value: {_POSIX_OPEN_MAX}
{PAGESIZE}
Size in bytes of a page.
Minimum Acceptable Value: 1
{PAGE_SIZE}
Equivalent to {PAGESIZE}. If either {PAGESIZE} or {PAGE_SIZE} is
defined, the other is defined with the same value.
{PTHREAD_DESTRUCTOR_ITERATIONS}
Maximum number of attempts made to destroy a thread's thread-spe-
cific data values on thread exit.
Minimum Acceptable Value: {_POSIX_THREAD_DESTRUCTOR_ITERATIONS}
{PTHREAD_KEYS_MAX}
Maximum number of data keys that can be created by a process.
Minimum Acceptable Value: {_POSIX_THREAD_KEYS_MAX}
{PTHREAD_STACK_MIN}
Minimum size in bytes of thread stack storage.
Minimum Acceptable Value: 0
{PTHREAD_THREADS_MAX}
Maximum number of threads that can be created per process.
Minimum Acceptable Value: {_POSIX_THREAD_THREADS_MAX}
{RE_DUP_MAX}
Maximum number of repeated occurrences of a BRE or ERE interval
expression; see Section 9.3.6, BREs Matching Multiple Characters
and Section 9.4.6, EREs Matching Multiple Characters.
Minimum Acceptable Value: {_POSIX2_RE_DUP_MAX}
{RTSIG_MAX}
Maximum number of realtime signals reserved for application use
in this implementation.
Minimum Acceptable Value: {_POSIX_RTSIG_MAX}
{SEM_NSEMS_MAX}
Maximum number of semaphores that a process may have.
Minimum Acceptable Value: {_POSIX_SEM_NSEMS_MAX}
{SEM_VALUE_MAX}
The maximum value a semaphore may have.
Minimum Acceptable Value: {_POSIX_SEM_VALUE_MAX}
{SIGQUEUE_MAX}
Maximum number of queued signals that a process may send and have
pending at the receiver(s) at any time.
Minimum Acceptable Value: {_POSIX_SIGQUEUE_MAX}
{SS_REPL_MAX}
The maximum number of replenishment operations that may be simul-
taneously pending for a particular sporadic server scheduler.
Minimum Acceptable Value: {_POSIX_SS_REPL_MAX}
{STREAM_MAX}
Maximum number of streams that one process can have open at one
time. If defined, it has the same value as {FOPEN_MAX} (see
<stdio.h>).
Minimum Acceptable Value: {_POSIX_STREAM_MAX}
{SYMLOOP_MAX}
Maximum number of symbolic links that can be reliably traversed
in the resolution of a pathname in the absence of a loop.
Minimum Acceptable Value: {_POSIX_SYMLOOP_MAX}
{TIMER_MAX}
Maximum number of timers per process supported by the implementa-
tion.
Minimum Acceptable Value: {_POSIX_TIMER_MAX}
{TRACE_EVENT_NAME_MAX}
Maximum length of the trace event name (not including the termi-
nating null).
Minimum Acceptable Value: {_POSIX_TRACE_EVENT_NAME_MAX}
{TRACE_NAME_MAX}
Maximum length of the trace generation version string or of the
trace stream name (not including the terminating null).
Minimum Acceptable Value: {_POSIX_TRACE_NAME_MAX}
{TRACE_SYS_MAX}
Maximum number of trace streams that may simultaneously exist in
the system.
Minimum Acceptable Value: {_POSIX_TRACE_SYS_MAX}
{TRACE_USER_EVENT_MAX}
Maximum number of user trace event type identifiers that may
simultaneously exist in a traced process, including the prede-
fined user trace event POSIX_TRACE_UNNAMED_USER_EVENT.
Minimum Acceptable Value: {_POSIX_TRACE_USER_EVENT_MAX}
{TTY_NAME_MAX}
Maximum length of terminal device name.
Minimum Acceptable Value: {_POSIX_TTY_NAME_MAX}
{TZNAME_MAX}
Maximum number of bytes supported for the name of a timezone (not
of the TZ variable).
Minimum Acceptable Value: {_POSIX_TZNAME_MAX}
Note: The length given by {TZNAME_MAX} does not include the quoting
characters mentioned in Section 8.3, Other Environment Vari-
ables.
Pathname Variable Values
The values in the following list may be constants within an implementa-
tion or may vary from one pathname to another. For example, file sys-
tems or directories may have different characteristics.
A definition of one of the symbolic constants in the following list
shall be omitted from the <limits.h> header on specific implementations
where the corresponding value is equal to or greater than the stated
minimum, but where the value can vary depending on the file to which it
is applied. The actual value supported for a specific pathname shall be
provided by the pathconf() function.
{FILESIZEBITS}
Minimum number of bits needed to represent, as a signed integer
value, the maximum size of a regular file allowed in the speci-
fied directory.
Minimum Acceptable Value: 32
{LINK_MAX}
Maximum number of links to a single file.
Minimum Acceptable Value: {_POSIX_LINK_MAX}
{MAX_CANON}
Maximum number of bytes in a terminal canonical input line.
Minimum Acceptable Value: {_POSIX_MAX_CANON}
{MAX_INPUT}
Minimum number of bytes for which space is available in a termi-
nal input queue; therefore, the maximum number of bytes a con-
forming application may require to be typed as input before read-
ing them.
Minimum Acceptable Value: {_POSIX_MAX_INPUT}
{NAME_MAX}
Maximum number of bytes in a filename (not including the termi-
nating null of a filename string).
Minimum Acceptable Value: {_POSIX_NAME_MAX}
Minimum Acceptable Value: {_XOPEN_NAME_MAX}
{PATH_MAX}
Maximum number of bytes the implementation will store as a path-
name in a user-supplied buffer of unspecified size, including the
terminating null character. Minimum number the implementation
will accept as the maximum number of bytes in a pathname.
Minimum Acceptable Value: {_POSIX_PATH_MAX}
Minimum Acceptable Value: {_XOPEN_PATH_MAX}
{PIPE_BUF}
Maximum number of bytes that is guaranteed to be atomic when
writing to a pipe.
Minimum Acceptable Value: {_POSIX_PIPE_BUF}
{POSIX_ALLOC_SIZE_MIN}
Minimum number of bytes of storage actually allocated for any
portion of a file.
Minimum Acceptable Value: Not specified.
{POSIX_REC_INCR_XFER_SIZE}
Recommended increment for file transfer sizes between the
{POSIX_REC_MIN_XFER_SIZE} and {POSIX_REC_MAX_XFER_SIZE} values.
Minimum Acceptable Value: Not specified.
{POSIX_REC_MAX_XFER_SIZE}
Maximum recommended file transfer size.
Minimum Acceptable Value: Not specified.
{POSIX_REC_MIN_XFER_SIZE}
Minimum recommended file transfer size.
Minimum Acceptable Value: Not specified.
{POSIX_REC_XFER_ALIGN}
Recommended file transfer buffer alignment.
Minimum Acceptable Value: Not specified.
{SYMLINK_MAX}
Maximum number of bytes in a symbolic link.
Minimum Acceptable Value: {_POSIX_SYMLINK_MAX}
Runtime Increasable Values
The magnitude limitations in the following list shall be fixed by spe-
cific implementations. An application should assume that the value of
the symbolic constant defined by <limits.h> in a specific implementa-
tion is the minimum that pertains whenever the application is run under
that implementation. A specific instance of a specific implementation
may increase the value relative to that supplied by <limits.h> for that
implementation. The actual value supported by a specific instance shall
be provided by the sysconf() function.
{BC_BASE_MAX}
Maximum obase values allowed by the bc utility.
Minimum Acceptable Value: {_POSIX2_BC_BASE_MAX}
{BC_DIM_MAX}
Maximum number of elements permitted in an array by the bc util-
ity.
Minimum Acceptable Value: {_POSIX2_BC_DIM_MAX}
{BC_SCALE_MAX}
Maximum scale value allowed by the bc utility.
Minimum Acceptable Value: {_POSIX2_BC_SCALE_MAX}
{BC_STRING_MAX}
Maximum length of a string constant accepted by the bc utility.
Minimum Acceptable Value: {_POSIX2_BC_STRING_MAX}
{CHARCLASS_NAME_MAX}
Maximum number of bytes in a character class name.
Minimum Acceptable Value: {_POSIX2_CHARCLASS_NAME_MAX}
{COLL_WEIGHTS_MAX}
Maximum number of weights that can be assigned to an entry of the
LC_COLLATE order keyword in the locale definition file; see Chap-
ter 7, Locale.
Minimum Acceptable Value: {_POSIX2_COLL_WEIGHTS_MAX}
{EXPR_NEST_MAX}
Maximum number of expressions that can be nested within parenthe-
ses by the expr utility.
Minimum Acceptable Value: {_POSIX2_EXPR_NEST_MAX}
{LINE_MAX}
Unless otherwise noted, the maximum length, in bytes, of a util-
ity'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>.
Minimum Acceptable Value: {_POSIX2_LINE_MAX}
{NGROUPS_MAX}
Maximum number of simultaneous supplementary group IDs per
process.
Minimum Acceptable Value: {_POSIX_NGROUPS_MAX}
{RE_DUP_MAX}
Maximum number of repeated occurrences of a regular expression
permitted when using the interval notation \{m,n\}; see Chapter
9, Regular Expressions.
Minimum Acceptable Value: {_POSIX2_RE_DUP_MAX}
Maximum Values
The <limits.h> header shall define the following symbolic constants
with the values shown. These are the most restrictive values for cer-
tain features on an implementation. A conforming implementation shall
provide values no larger than these values. A conforming application
must not require a smaller value for correct operation.
{_POSIX_CLOCKRES_MIN}
The resolution of the CLOCK_REALTIME clock, in nanoseconds.
Value: 20 000 000
If the Monotonic Clock option is supported, the resolution of the
CLOCK_MONOTONIC clock, in nanoseconds, is represented by
{_POSIX_CLOCKRES_MIN}.
Minimum Values
The <limits.h> header shall define the following symbolic constants
with the values shown. These are the most restrictive values for cer-
tain features on an implementation conforming to this volume of
POSIX.1-2008. Related symbolic constants are defined elsewhere in this
volume of POSIX.1-2008 which reflect the actual implementation and
which need not be as restrictive. For each of these limits, a conform-
ing implementation shall provide a value at least this large or shall
have no limit. A strictly conforming application must not require a
larger value for correct operation.
{_POSIX_AIO_LISTIO_MAX}
The number of I/O operations that can be specified in a list I/O
call.
Value: 2
{_POSIX_AIO_MAX}
The number of outstanding asynchronous I/O operations.
Value: 1
{_POSIX_ARG_MAX}
Maximum length of argument to the exec functions including envi-
ronment data.
Value: 4 096
{_POSIX_CHILD_MAX}
Maximum number of simultaneous processes per real user ID.
Value: 25
{_POSIX_DELAYTIMER_MAX}
The number of timer expiration overruns.
Value: 32
{_POSIX_HOST_NAME_MAX}
Maximum length of a host name (not including the terminating
null) as returned from the gethostname() function.
Value: 255
{_POSIX_LINK_MAX}
Maximum number of links to a single file.
Value: 8
{_POSIX_LOGIN_NAME_MAX}
The size of the storage required for a login name, in bytes
(including the terminating null).
Value: 9
{_POSIX_MAX_CANON}
Maximum number of bytes in a terminal canonical input queue.
Value: 255
{_POSIX_MAX_INPUT}
Maximum number of bytes allowed in a terminal input queue.
Value: 255
{_POSIX_MQ_OPEN_MAX}
The number of message queues that can be open for a single
process.
Value: 8
{_POSIX_MQ_PRIO_MAX}
The maximum number of message priorities supported by the imple-
mentation.
Value: 32
{_POSIX_NAME_MAX}
Maximum number of bytes in a filename (not including the termi-
nating null of a filename string).
Value: 14
{_POSIX_NGROUPS_MAX}
Maximum number of simultaneous supplementary group IDs per
process.
Value: 8
{_POSIX_OPEN_MAX}
A value one greater than the maximum value that the system may
assign to a newly-created file descriptor.
Value: 20
{_POSIX_PATH_MAX}
Minimum number the implementation will accept as the maximum num-
ber of bytes in a pathname.
Value: 256
{_POSIX_PIPE_BUF}
Maximum number of bytes that is guaranteed to be atomic when
writing to a pipe.
Value: 512
{_POSIX_RE_DUP_MAX}
The number of repeated occurrences of a BRE permitted by the
regexec() and regcomp() functions when using the interval nota-
tion {\(m,n\}; see Section 9.3.6, BREs Matching Multiple Charac-
ters.
Value: 255
{_POSIX_RTSIG_MAX}
The number of realtime signal numbers reserved for application
use.
Value: 8
{_POSIX_SEM_NSEMS_MAX}
The number of semaphores that a process may have.
Value: 256
{_POSIX_SEM_VALUE_MAX}
The maximum value a semaphore may have.
Value: 32 767
{_POSIX_SIGQUEUE_MAX}
The number of queued signals that a process may send and have
pending at the receiver(s) at any time.
Value: 32
{_POSIX_SSIZE_MAX}
The value that can be stored in an object of type ssize_t.
Value: 32 767
{_POSIX_SS_REPL_MAX}
The number of replenishment operations that may be simultaneously
pending for a particular sporadic server scheduler.
Value: 4
{_POSIX_STREAM_MAX}
The number of streams that one process can have open at one time.
Value: 8
{_POSIX_SYMLINK_MAX}
The number of bytes in a symbolic link.
Value: 255
{_POSIX_SYMLOOP_MAX}
The number of symbolic links that can be traversed in the resolu-
tion of a pathname in the absence of a loop.
Value: 8
{_POSIX_THREAD_DESTRUCTOR_ITERATIONS}
The number of attempts made to destroy a thread's thread-specific
data values on thread exit.
Value: 4
{_POSIX_THREAD_KEYS_MAX}
The number of data keys per process.
Value: 128
{_POSIX_THREAD_THREADS_MAX}
The number of threads per process.
Value: 64
{_POSIX_TIMER_MAX}
The per-process number of timers.
Value: 32
{_POSIX_TRACE_EVENT_NAME_MAX}
The length in bytes of a trace event name (not including the ter-
minating null).
Value: 30
{_POSIX_TRACE_NAME_MAX}
The length in bytes of a trace generation version string or a
trace stream name (not including the terminating null).
Value: 8
{_POSIX_TRACE_SYS_MAX}
The number of trace streams that may simultaneously exist in the
system.
Value: 8
{_POSIX_TRACE_USER_EVENT_MAX}
The number of user trace event type identifiers that may simulta-
neously exist in a traced process, including the predefined user
trace event POSIX_TRACE_UNNAMED_USER_EVENT.
Value: 32
{_POSIX_TTY_NAME_MAX}
The size of the storage required for a terminal device name, in
bytes (including the terminating null).
Value: 9
{_POSIX_TZNAME_MAX}
Maximum number of bytes supported for the name of a timezone (not
of the TZ variable).
Value: 6
Note: The length given by {_POSIX_TZNAME_MAX} does not
include the quoting characters mentioned in Section
8.3, Other Environment Variables.
{_POSIX2_BC_BASE_MAX}
Maximum obase values allowed by the bc utility.
Value: 99
{_POSIX2_BC_DIM_MAX}
Maximum number of elements permitted in an array by the bc util-
ity.
Value: 2 048
{_POSIX2_BC_SCALE_MAX}
Maximum scale value allowed by the bc utility.
Value: 99
{_POSIX2_BC_STRING_MAX}
Maximum length of a string constant accepted by the bc utility.
Value: 1 000
{_POSIX2_CHARCLASS_NAME_MAX}
Maximum number of bytes in a character class name.
Value: 14
{_POSIX2_COLL_WEIGHTS_MAX}
Maximum number of weights that can be assigned to an entry of the
LC_COLLATE order keyword in the locale definition file; see Chap-
ter 7, Locale.
Value: 2
{_POSIX2_EXPR_NEST_MAX}
Maximum number of expressions that can be nested within parenthe-
ses by the expr utility.
Value: 32
{_POSIX2_LINE_MAX}
Unless otherwise noted, the maximum length, in bytes, of a util-
ity'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>.
Value: 2 048
{_POSIX2_RE_DUP_MAX}
Maximum number of repeated occurrences of a regular expression
permitted when using the interval notation \{m,n\}; see Chapter
9, Regular Expressions.
Value: 255
{_XOPEN_IOV_MAX}
Maximum number of iovec structures that one process has available
for use with readv() or writev().
Value: 16
{_XOPEN_NAME_MAX}
Maximum number of bytes in a filename (not including the termi-
nating null of a filename string).
Value: 255
{_XOPEN_PATH_MAX}
Minimum number the implementation will accept as the maximum num-
ber of bytes in a pathname.
Value: 1024
Numerical Limits
The <limits.h> header shall define the following macros and, except for
{CHAR_BIT}, {LONG_BIT}, {MB_LEN_MAX}, and {WORD_BIT}, they shall be
replaced by expressions that have the same type as would an expression
that is an object of the corresponding type converted according to the
integer promotions.
If the value of an object of type char is treated as a signed integer
when used in an expression, the value of {CHAR_MIN} is the same as that
of {SCHAR_MIN} and the value of {CHAR_MAX} is the same as that of
{SCHAR_MAX}. Otherwise, the value of {CHAR_MIN} is 0 and the value of
{CHAR_MAX} is the same as that of {UCHAR_MAX}.
{CHAR_BIT}
Number of bits in a type char.
Value: 8
{CHAR_MAX}
Maximum value for an object of type char.
Value: {UCHAR_MAX} or {SCHAR_MAX}
{CHAR_MIN}
Minimum value for an object of type char.
Value: {SCHAR_MIN} or 0
{INT_MAX}
Maximum value for an object of type int.
Minimum Acceptable Value: 2 147 483 647
{INT_MIN}
Minimum value for an object of type int.
Maximum Acceptable Value: -2 147 483 647
{LLONG_MAX}
Maximum value for an object of type long long.
Minimum Acceptable Value: +9223372036854775807
{LLONG_MIN}
Minimum value for an object of type long long.
Maximum Acceptable Value: -9223372036854775807
{LONG_BIT}
Number of bits in an object of type long.
Minimum Acceptable Value: 32
{LONG_MAX}
Maximum value for an object of type long.
Minimum Acceptable Value: +2 147 483 647
{LONG_MIN}
Minimum value for an object of type long.
Maximum Acceptable Value: -2 147 483 647
{MB_LEN_MAX}
Maximum number of bytes in a character, for any supported locale.
Minimum Acceptable Value: 1
{SCHAR_MAX}
Maximum value for an object of type signed char.
Value: +127
{SCHAR_MIN}
Minimum value for an object of type signed char.
Value: -128
{SHRT_MAX}
Maximum value for an object of type short.
Minimum Acceptable Value: +32 767
{SHRT_MIN}
Minimum value for an object of type short.
Maximum Acceptable Value: -32 767
{SSIZE_MAX}
Maximum value for an object of type ssize_t.
Minimum Acceptable Value: {_POSIX_SSIZE_MAX}
{UCHAR_MAX}
Maximum value for an object of type unsigned char.
Value: 255
{UINT_MAX}
Maximum value for an object of type unsigned.
Minimum Acceptable Value: 4 294 967 295
{ULLONG_MAX}
Maximum value for an object of type unsigned long long.
Minimum Acceptable Value: 18446744073709551615
{ULONG_MAX}
Maximum value for an object of type unsigned long.
Minimum Acceptable Value: 4 294 967 295
{USHRT_MAX}
Maximum value for an object of type unsigned short.
Minimum Acceptable Value: 65 535
{WORD_BIT}
Number of bits in an object of type int.
Minimum Acceptable Value: 32
Other Invariant Values
The <limits.h> header shall define the following symbolic constants:
{NL_ARGMAX}
Maximum value of n in conversion specifications using the "%n$"
sequence in calls to the printf() and scanf() families of func-
tions.
Minimum Acceptable Value: 9
{NL_LANGMAX}
Maximum number of bytes in a LANG name.
Minimum Acceptable Value: 14
{NL_MSGMAX}
Maximum message number.
Minimum Acceptable Value: 32 767
{NL_SETMAX}
Maximum set number.
Minimum Acceptable Value: 255
{NL_TEXTMAX}
Maximum number of bytes in a message string.
Minimum Acceptable Value: {_POSIX2_LINE_MAX}
{NZERO}
Default process priority.
Minimum Acceptable Value: 20
The following sections are informative.
APPLICATION USAGE
None.
RATIONALE
A request was made to reduce the value of {_POSIX_LINK_MAX} from the
value of 8 specified for it in the POSIX.1-1990 standard to 2. The
standard developers decided to deny this request for several reasons:
* They wanted to avoid making any changes to the standard that could
break conforming applications, and the requested change could have
that effect.
* The use of multiple hard links to a file cannot always be replaced
with use of symbolic links. Symbolic links are semantically differ-
ent from hard links in that they associate a pathname with another
pathname rather than a pathname with a file. This has implications
for access control, file permanence, and transparency.
* The original standard developers had considered the issue of allow-
ing for implementations that did not in general support hard links,
and decided that this would reduce consensus on the standard.
Systems that support historical versions of the development option of
the ISO POSIX-2 standard retain the name {_POSIX2_RE_DUP_MAX} as an
alias for {_POSIX_RE_DUP_MAX}.
{PATH_MAX}
IEEE PASC Interpretation 1003.1 #15 addressed the inconsistency
in the standard with the definition of pathname and the descrip-
tion of {PATH_MAX}, allowing application developers to allocate
either {PATH_MAX} or {PATH_MAX}+1 bytes. The inconsistency has
been removed by correction to the {PATH_MAX} definition to
include the null character. With this change, applications that
previously allocated {PATH_MAX} bytes will continue to succeed.
{SYMLINK_MAX}
This symbol refers to space for data that is stored in the file
system, as opposed to {PATH_MAX} which is the length of a name
that can be passed to a function. In some existing implementa-
tions, the pathnames pointed to by symbolic links are stored in
the inodes of the links, so it is important that {SYMLINK_MAX}
not be constrained to be as large as {PATH_MAX}.
FUTURE DIRECTIONS
None.
SEE ALSO
Chapter 7, Locale, <stdio.h>, <unistd.h>
The System Interfaces volume of POSIX.1-2008, Section 2.2, The Compila-
tion Environment, fpathconf(), sysconf()
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri-
cal and Electronics Engineers, Inc and The Open Group. (This is
POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the source
files to man page format. To report such errors, see https://www.ker-
nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 limits.h(0P)
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