ftruncate(3p) — Linux manual page


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

PROLOG         top

       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         top

       ftruncate — truncate a file to a specified length

SYNOPSIS         top

       #include <unistd.h>

       int ftruncate(int fildes, off_t length);

DESCRIPTION         top

       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

RETURN VALUE         top

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

ERRORS         top

       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

       EBADF or EINVAL
              The fildes argument is not a file descriptor open for writing.

       The following sections are informative.

EXAMPLES         top




RATIONALE         top




SEE ALSO         top

       open(3p), truncate(3p)

       The Base Definitions volume of POSIX.1‐2008, unistd.h(0p)

COPYRIGHT         top

       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 .

       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 .

IEEE/The Open Group                 2013                       FTRUNCATE(3P)

Pages that refer to this page: unistd.h(0p)posix_fallocate(3p)posix_typed_mem_open(3p)