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 correspond-
       ing 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 ftruncate() 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 modi-
       fied 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 Technol-
       ogy -- 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)