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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 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,  ftrun-
       cate()  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 unsuc-
       cessful, 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 SIG-
       BUS 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>
COPYRIGHT
       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 Electri-
       cal  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.ker-
       nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group                  2013                        FTRUNCATE(3P)