<limits.h>(P) POSIX Programmer's Manual <limits.h>(P)
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.
NAMElimits.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 IEEE Std 1003.1-2001, Sec‐
tion 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.
The <limits.h> header shall define various symbolic names. Different
categories of names are described below.
The names represent various limits on resources that the implementation
imposes on applications.
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
application wishing to avail itself of the full amount of a resource
available on an implementation may make use of the value given in <lim‐
its.h> on that particular implementation, by using the symbolic names
listed below. It should be noted, however, that many of the listed lim‐
its are not invariant, and at runtime, the value of the limit may dif‐
fer 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 names in the following list shall
be omitted from <limits.h> on specific implementations where the corre‐
sponding 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 avail‐
able 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}
Maximum number of files that one process can have open at any
one time.
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-
specific 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}
The number of repeated occurrences of a BRE permitted by the
regexec() and regcomp() functions when using the interval nota‐
tion {\(m,n\}; see BREs 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
simultaneously pending for a particular sporadic server sched‐
uler.
Minimum Acceptable Value: {_POSIX_SS_REPL_MAX}
{STREAM_MAX}
The 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 implemen‐
tation.
Minimum Acceptable Value: {_POSIX_TIMER_MAX}
{TRACE_EVENT_NAME_MAX}
Maximum length of the trace event name.
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.
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 Other Environment Variables .
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 values 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
reading them.
Minimum Acceptable Value: {_POSIX_MAX_INPUT}
{NAME_MAX}
Maximum number of bytes in a filename (not including terminating
null).
Minimum Acceptable Value: {_POSIX_NAME_MAX}
Minimum Acceptable Value: {_XOPEN_NAME_MAX}
{PATH_MAX}
Maximum number of bytes in a pathname, including the terminating
null character.
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 sup‐
plied by <limits.h> in a specific implementation 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
Locale .
Minimum Acceptable Value: {_POSIX2_COLL_WEIGHTS_MAX}
{EXPR_NEST_MAX}
Maximum number of expressions that can be nested within paren‐
theses 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 Regular
Expressions .
Minimum Acceptable Value: {_POSIX2_RE_DUP_MAX}
Maximum Values
The symbolic constants in the following list shall be defined in <lim‐
its.h> with the values shown. These are symbolic names for the most
restrictive value for certain features on an implementation supporting
the Timers option. 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_CLOCK‐
RES_MIN}.
Minimum Values
The symbolic constants in the following list shall be defined in <lim‐
its.h> with the values shown. These are symbolic names for the most
restrictive value for certain features on an implementation conforming
to this volume of IEEE Std 1003.1-2001. Related symbolic constants are
defined elsewhere in this volume of IEEE Std 1003.1-2001 which reflect
the actual implementation and which need not be as restrictive. A con‐
forming implementation shall provide values at least this large. 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 terminating
null).
Value: 14
{_POSIX_NGROUPS_MAX}
Maximum number of simultaneous supplementary group IDs per
process.
Value: 8
{_POSIX_OPEN_MAX}
Maximum number of files that one process can have open at any
one time.
Value: 20
{_POSIX_PATH_MAX}
Maximum number 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 BREs Matching Multiple Characters .
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_STREAM_MAX}
The number of streams that one process can have open at one
time.
Value: 8
{_POSIX_SS_REPL_MAX}
The number of replenishment operations that may be simultane‐
ously pending for a particular sporadic server scheduler.
Value: 4
{_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 reso‐
lution 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-spe‐
cific 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.
Value: 30
{_POSIX_TRACE_NAME_MAX}
The length in bytes of a trace generation version string or a
trace stream name.
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 simul‐
taneously 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 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
Locale .
Value: 2
{_POSIX2_EXPR_NEST_MAX}
Maximum number of expressions that can be nested within paren‐
theses 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 Regular
Expressions .
Value: 255
{_XOPEN_IOV_MAX}
Maximum number of iovec structures that one process has avail‐
able for use with readv() or writev().
Value: 16
{_XOPEN_NAME_MAX}
Maximum number of bytes in a filename (not including the termi‐
nating null).
Value: 255
{_XOPEN_PATH_MAX}
Maximum number of bytes in a pathname.
Value: 1024
Numerical Limits
The values in the following lists shall be defined in <limits.h> and
are constant expressions suitable for use in #if preprocessing direc‐
tives. Moreover, except for {CHAR_BIT}, {DBL_DIG}, {DBL_MAX},
{FLT_DIG}, {FLT_MAX}, {LONG_BIT}, {WORD_BIT}, and {MB_LEN_MAX}, the
symbolic names are defined as expressions of the correct type.
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 of type char.
Value: {UCHAR_MAX} or {SCHAR_MAX}
{CHAR_MIN}
Minimum value of type char.
Value: {SCHAR_MIN} or 0
{INT_MAX}
Maximum value of an int.
Minimum Acceptable Value: 2 147 483 647
{LONG_BIT}
Number of bits in a long.
Minimum Acceptable Value: 32
{LONG_MAX}
Maximum value of a long.
Minimum 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 of type signed char.
Value: +127
{SHRT_MAX}
Maximum value of type short.
Minimum Acceptable Value: +32 767
{SSIZE_MAX}
Maximum value of an object of type ssize_t.
Minimum Acceptable Value: {_POSIX_SSIZE_MAX}
{UCHAR_MAX}
Maximum value of type unsigned char.
Value: 255
{UINT_MAX}
Maximum value of type unsigned.
Minimum Acceptable Value: 4 294 967 295
{ULONG_MAX}
Maximum value of type unsigned long.
Minimum Acceptable Value: 4 294 967 295
{USHRT_MAX}
Maximum value for a type unsigned short.
Minimum Acceptable Value: 65 535
{WORD_BIT}
Number of bits in a word or type int.
Minimum Acceptable Value: 16
{INT_MIN}
Minimum value of type int.
Maximum Acceptable Value: -2 147 483 647
{LONG_MIN}
Minimum value of type long.
Maximum Acceptable Value: -2 147 483 647
{SCHAR_MIN}
Minimum value of type signed char.
Value: -128
{SHRT_MIN}
Minimum value of type short.
Maximum Acceptable Value: -32 767
{LLONG_MIN}
Minimum value of type long long.
Maximum Acceptable Value: -9223372036854775807
{LLONG_MAX}
Maximum value of type long long.
Minimum Acceptable Value: +9223372036854775807
{ULLONG_MAX}
Maximum value of type unsigned long long.
Minimum Acceptable Value: 18446744073709551615
Other Invariant Values
The following constants shall be defined on all implementations in
<limits.h>:
{CHARCLASS_NAME_MAX}
Maximum number of bytes in a character class name.
Minimum Acceptable Value: 14
{NL_ARGMAX}
Maximum value of digit in calls to the printf() and scanf()
functions.
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_NMAX}
Maximum number of bytes in an N-to-1 collation mapping.
Minimum Acceptable Value: No guaranteed value across all con‐
forming implementations.
{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 writers 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 filenames 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
The System Interfaces volume of IEEE Std 1003.1-2001, fpathconf(),
pathconf(), sysconf()COPYRIGHT
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 .
IEEE/The Open Group 2003 <limits.h>(P)
