ftruncate man page on Oracle

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FTRUNCATE(3P)		   POSIX Programmer's Manual		 FTRUNCATE(3P)

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
       ftruncate - truncate a file to a specified length

SYNOPSIS
       #include <unistd.h>

       int ftruncate(int fildes, off_t length);

DESCRIPTION
       If fildes is not a valid file descriptor open for writing,  the	ftrun‐
       cate() function shall fail.

       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 unspecified.

       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 undefined.

       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.

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

ERRORS
       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 established 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.

EXAMPLES
       None.

APPLICATION USAGE
       None.

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

FUTURE DIRECTIONS
       None.

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

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			 FTRUNCATE(3P)
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