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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, provided 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 <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 implementations, 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 supported by the
implementation.
Minimum Acceptable Value: {_POSIX_AIO_LISTIO_MAX}
{AIO_MAX}
Maximum number of outstanding asynchronous I/O operations supported by the
implementation.
Minimum Acceptable Value: {_POSIX_AIO_MAX}
{AIO_PRIO_DELTA_MAX}
The maximum amount by which a process can decrease its asynchronous I/O priority
level from its own scheduling priority.
Minimum Acceptable Value: 0
{ARG_MAX}
Maximum length of argument to the exec functions including environment 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 implementation.
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-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}
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 simultaneously 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 implementation.
Minimum Acceptable Value: {_POSIX_TIMER_MAX}
{TRACE_EVENT_NAME_MAX}
Maximum length of the trace event name (not including the terminating 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 predefined 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 Variables.
Pathname Variable Values
The values in the following list may be constants within an implementation or may vary
from one pathname to another. For example, file systems 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 specified 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 terminal input queue;
therefore, the maximum number of bytes a conforming 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 the terminating 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 pathname 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 specific
implementations. An application should assume that the value of the symbolic constant
defined 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 utility.
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 Chapter 7, Locale.
Minimum Acceptable Value: {_POSIX2_COLL_WEIGHTS_MAX}
{EXPR_NEST_MAX}
Maximum number of expressions that can be nested within parentheses by the expr
utility.
Minimum Acceptable Value: {_POSIX2_EXPR_NEST_MAX}
{LINE_MAX}
Unless otherwise noted, the maximum length, in bytes, of a utility'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 certain 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 certain 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 conforming 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 environment 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 implementation.
Value: 32
{_POSIX_NAME_MAX}
Maximum number of bytes in a filename (not including the terminating 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 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 notation {\(m,n\}; see Section 9.3.6, 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_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 resolution 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 terminating 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 simultaneously 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 utility.
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 Chapter 7, Locale.
Value: 2
{_POSIX2_EXPR_NEST_MAX}
Maximum number of expressions that can be nested within parentheses by the expr
utility.
Value: 32
{_POSIX2_LINE_MAX}
Unless otherwise noted, the maximum length, in bytes, of a utility'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 terminating null of a
filename string).
Value: 255
{_XOPEN_PATH_MAX}
Minimum number the implementation will accept as the maximum number 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 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_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 different 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 allowing 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 description 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 implementations, 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 Compilation 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 Electrical 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.kernel.org/doc/man-pages/reporting_bugs.html .