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 object.

RETURN VALUE         top

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

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

       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

       The following sections are informative.

EXAMPLES         top




RATIONALE         top




SEE ALSO         top

       open(3p), truncate(3p)

       The Base Definitions volume of POSIX.1‐2017, unistd.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic
       form from IEEE Std 1003.1-2017, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The
       Open Group Base Specifications Issue 7, 2018 Edition, Copyright
       (C) 2018 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 .

       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               2017                     FTRUNCATE(3P)

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