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.
limits.h — implementation-defined constants
#include <limits.h>
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.1-2017, 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.
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}
{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. |
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}
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 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: {_POSIX_RE_DUP_MAX}
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}.
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.1-2017. Related symbolic
constants are defined elsewhere in this volume of
POSIX.1-2017 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}
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.
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 BRE or ERE interval expression; see
Section 9.3.6, BREs Matching Multiple
Characters and Section 9.4.6, EREs Matching
Multiple Characters.
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
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
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.
None.
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}.
None.
Chapter 7, Locale, <stdio.h>, <unistd.h>
The System Interfaces volume of POSIX.1-2017, Section 2.2, The Compilation Environment, fpathconf(), sysconf()
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .
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 .