# ftruncate

## 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.
    


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