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Linux 2.6 - man page for ftruncate (linux section 3posix)

FTRUNCATE(P)			    POSIX Programmer's Manual			     FTRUNCATE(P)

       ftruncate - truncate a file to a specified length

       #include <unistd.h>

       int ftruncate(int fildes, off_t length);

       If  fildes is not a valid file descriptor open for writing, the ftruncate() function shall

       If fildes refers to a regular file, the ftruncate() function shall cause the size  of  the
       file  to  be  truncated to length. If the size of the file previously exceeded length, the
       extra data shall no longer be available to reads on the file. If the file  previously  was
       smaller	than  this  size, ftruncate() shall either increase the size of the file or fail.
	XSI-conformant systems shall increase the  size  of  the  file.   If  the  file  size  is
       increased, the extended area shall appear as if it were zero-filled. The value of the seek
       pointer shall not be modified by a call to ftruncate().

       Upon successful completion, if fildes refers to a regular file, the  ftruncate()  function
       shall  mark  for  update  the st_ctime and st_mtime fields of the file and the S_ISUID and
       S_ISGID bits of the file mode may be cleared. If the ftruncate() function is unsuccessful,
       the file is unaffected.

       If  the	request  would	cause  the  file  size to exceed the soft file size limit for the
       process, the request shall fail and the implementation shall generate the  SIGXFSZ  signal
       for the thread.

       If fildes refers to a directory, ftruncate() shall fail.

       If  fildes  refers  to  any  other file type, except a shared memory object, the result is

       If fildes refers to a shared memory object, ftruncate() shall set the size of  the  shared
       memory object to length.

       If  the	effect of ftruncate() is to decrease the size of a shared memory object or memory
       mapped file and whole pages beyond the new end were  previously	mapped,  then  the  whole
       pages beyond the new end shall be discarded.

       If  the	Memory Protection option is supported, references to discarded pages shall result
       in the generation of a SIGBUS signal; otherwise, the result of such  references	is  unde-

       If  the	effect	of  ftruncate()  is to increase the size of a shared memory object, it is
       unspecified whether the contents of any mapped pages between the old end-of-file  and  the
       new are flushed to the underlying object.

       Upon  successful  completion,  ftruncate() shall return 0; otherwise, -1 shall be returned
       and errno set to indicate the error.

       The ftruncate() function shall fail if:

       EINTR  A signal was caught during execution.

       EINVAL The length argument was less than 0.

       EFBIG or EINVAL

	      The length argument was greater than the maximum file size.

       EFBIG  The file is a regular file and length is greater than  the  offset  maximum  estab-
	      lished in the open file description associated with fildes.

       EIO    An I/O error occurred while reading from or writing to a file system.

       EBADF or EINVAL

	      The fildes argument is not a file descriptor open for writing.

       EINVAL The fildes argument references a file that was opened without write permission.

       EROFS  The named file resides on a read-only file system.

       The following sections are informative.



       The  ftruncate() function is part of IEEE Std 1003.1-2001 as it was deemed to be more use-
       ful than truncate(). The truncate() function is provided as an XSI extension.


       open() , truncate() , the Base Definitions volume of IEEE Std 1003.1-2001, <unistd.h>

       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 orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003				     FTRUNCATE(P)

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