Name
truncate, ftruncate — truncate a file to a specified
length
Synopsis
int
truncate( |
const char * |
path, |
| |
off_t |
length); |
int
ftruncate( |
int |
fd, |
| |
off_t |
length); |
DESCRIPTION
The truncate() and
ftruncate() functions cause the
regular file named by path or referenced by
fd to be truncated to
a size of precisely length bytes.
If the file previously was larger than this size, the
extra data is lost. If the file previously was shorter, it is
extended, and the extended part reads as null bytes
('\0').
The file offset is not changed.
If the size changed, then the st_ctime and st_mtime fields
(respectively, time of last status change and time of last
modification; see stat(2)) for the file are
updated, and the set-user-ID and set-group-ID permission bits
may be cleared.
With ftruncate(), the file
must be open for writing; with truncate(), the file must be writable.
RETURN VALUE
On success, zero is returned. On error, −1 is
returned, and errno is set
appropriately.
ERRORS
For truncate():
- EACCES
-
Search permission is denied for a component of the
path prefix, or the named file is not writable by the
user. (See also path_resolution(7).)
- EFAULT
-
Path
points outside the process's allocated address
space.
- EFBIG
-
The argument length is larger than the
maximum file size. (XSI)
- EINTR
-
A signal was caught during execution.
- EINVAL
-
The argument length is negative or
larger than the maximum file size.
- EIO
-
An I/O error occurred updating the inode.
- EISDIR
-
The named file is a directory.
- ELOOP
-
Too many symbolic links were encountered in
translating the pathname.
- ENAMETOOLONG
-
A component of a pathname exceeded 255 characters,
or an entire pathname exceeded 1023 characters.
- ENOENT
-
The named file does not exist.
- ENOTDIR
-
A component of the path prefix is not a
directory.
- EPERM
-
The underlying file system does not support
extending a file beyond its current size.
- EROFS
-
The named file resides on a read-only file
system.
- ETXTBSY
-
The file is a pure procedure (shared text) file that
is being executed.
For ftruncate() the same
errors apply, but instead of things that can be wrong with
path, we now have
things that can be wrong with fd:
- EBADF
-
The fd is
not a valid descriptor.
- EBADF or EINVAL
-
The fd is
not open for writing.
- EINVAL
-
The fd does
not reference a regular file.
CONFORMING TO
4.4BSD, SVr4, POSIX.1-2001 (these calls first appeared in
4.2BSD).
NOTES
The above description is for XSI-compliant systems. For
non-XSI-compliant systems, the POSIX standard allows two
behaviours for ftruncate() when
length exceeds the
file length (note that truncate() is not specified at all in such
an environment): either returning an error, or extending the
file. Like most Unix implementations, Linux follows the XSI
requirement when dealing with native file systems. However,
some non-native file systems do not permit truncate() and ftruncate() to be used to extend a file
beyond its current length: a notable example on Linux is
VFAT.
SEE ALSO
open(2), stat(2), path_resolution(7)
Copyright (c) 1983, 1991 The Regents of the University of California.
All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.
3. All advertising materials mentioning features or use of this software
must display the following acknowledgement:
This product includes software developed by the University of
California, Berkeley and its contributors.
4. Neither the name of the University nor the names of its contributors
may be used to endorse or promote products derived from this software
without specific prior written permission.
THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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SUCH DAMAGE.
@(#)truncate.2
6.9 (Berkeley) 3/10/91
Modified 1993-07-24 by Rik Faith <faith@cs.unc.edu>
Modified 1996-10-22 by Eric S. Raymond <esr@thyrsus.com>
Modified 1998-12-21 by Andries Brouwer <aeb@cwi.nl>
Modified 2002-01-07 by Michael Kerrisk <mtk-manpages@gmx.net>
Modified 2002-04-06 by Andries Brouwer <aeb@cwi.nl>
Modified 2004-06-23 by Michael Kerrisk <mtk-manpages@gmx.net>
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