FTRUNCATE
Section: POSIX Programmer's Manual (3P)
Updated: 2013
Index
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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>
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
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 .
Index
- PROLOG
-
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- EXAMPLES
-
- APPLICATION USAGE
-
- RATIONALE
-
- FUTURE DIRECTIONS
-
- SEE ALSO
-
- COPYRIGHT
-
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