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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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FTRUNCATE(3P) POSIX Programmer's Manual FTRUNCATE(3P)
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.
ftruncate — truncate a file to a specified length
#include <unistd.h>
int ftruncate(int fildes, off_t length);
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.
Upon successful completion, ftruncate() shall return 0; otherwise,
-1 shall be returned and errno set to indicate the error.
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.
None.
None.
None.
None.
open(3p), truncate(3p)
The Base Definitions volume of POSIX.1‐2017, unistd.h(0p)
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
http://www.opengroup.org/unix/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 .
IEEE/The Open Group 2017 FTRUNCATE(3P)
Pages that refer to this page: unistd.h(0p), posix_fallocate(3p), posix_typed_mem_open(3p)
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HTML rendering created 2025-02-02 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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