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32.6 Limits on File System Capacity
===================================
The POSIX.1 standard specifies a number of parameters that describe the
limitations of the file system. It's possible for the system to have a
fixed, uniform limit for a parameter, but this isn't the usual case. On
most systems, it's possible for different file systems (and, for some
parameters, even different files) to have different maximum limits. For
example, this is very likely if you use NFS to mount some of the file
systems from other machines.
Each of the following macros is defined in 'limits.h' only if the
system has a fixed, uniform limit for the parameter in question. If the
system allows different file systems or files to have different limits,
then the macro is undefined; use 'pathconf' or 'fpathconf' to find out
the limit that applies to a particular file. Pathconf.
Each parameter also has another macro, with a name starting with
'_POSIX', which gives the lowest value that the limit is allowed to have
on _any_ POSIX system. File Minimums.
-- Macro: int LINK_MAX
The uniform system limit (if any) for the number of names for a
given file. Hard Links.
-- Macro: int MAX_CANON
The uniform system limit (if any) for the amount of text in a line
of input when input editing is enabled. Canonical or Not.
-- Macro: int MAX_INPUT
The uniform system limit (if any) for the total number of
characters typed ahead as input. I/O Queues.
-- Macro: int NAME_MAX
The uniform system limit (if any) for the length of a file name
component, not including the terminating null character.
*Portability Note:* On some systems, the GNU C Library defines
'NAME_MAX', but does not actually enforce this limit.
-- Macro: int PATH_MAX
The uniform system limit (if any) for the length of an entire file
name (that is, the argument given to system calls such as 'open'),
including the terminating null character.
*Portability Note:* The GNU C Library does not enforce this limit
even if 'PATH_MAX' is defined.
-- Macro: int PIPE_BUF
The uniform system limit (if any) for the number of bytes that can
be written atomically to a pipe. If multiple processes are writing
to the same pipe simultaneously, output from different processes
might be interleaved in chunks of this size. Pipes and
FIFOs.
These are alternative macro names for some of the same information.
-- Macro: int MAXNAMLEN
This is the BSD name for 'NAME_MAX'. It is defined in 'dirent.h'.
-- Macro: int FILENAME_MAX
The value of this macro is an integer constant expression that
represents the maximum length of a file name string. It is defined
in 'stdio.h'.
Unlike 'PATH_MAX', this macro is defined even if there is no actual
limit imposed. In such a case, its value is typically a very large
number. *This is always the case on GNU/Hurd systems.*
*Usage Note:* Don't use 'FILENAME_MAX' as the size of an array in
which to store a file name! You can't possibly make an array that
big! Use dynamic allocation ( Memory Allocation) instead.
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