bionic (3) ftruncate.3posix.gz

Provided by: manpages-posix-dev_2013a-2_all bug

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 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
       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, ftruncate() shall mark for update the
       last data modification and last file status change timestamps 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 memory mapped file or a  shared  memory  object
       and  whole pages beyond the new end were previously mapped, then the whole pages beyond the new end shall
       be discarded.

       References to discarded pages shall result in the generation of a SIGBUS signal.

       If the effect of ftruncate() is to increase the size of a 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.

       The following sections are informative.


EXAMPLES
       None.


APPLICATION USAGE
       None.


RATIONALE
       None.


FUTURE DIRECTIONS
       None.


SEE ALSO
       open(), truncate()

       The Base Definitions volume of POSIX.1‐2008, <unistd.h>


       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition,
       Standard  for  Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers,  Inc
       and  The  Open Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/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 .