Name

truncate, ftruncate — truncate a file to a specified length

Synopsis

#include <unistd.h>
#include <sys/types.h>
int truncate( const char *path,
  off_t length);
 
int ftruncate( int fd,
  off_t length);
 
[Note] Note
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
truncate():
_BSD_SOURCE || _XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
|| /* Since glibc 2.12: */
_POSIX_C_SOURCE >= 200809L
ftruncate():
_BSD_SOURCE || _XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
|| /* Since glibc 2.3.5: */
_POSIX_C_SOURCE >= 200112L

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

While blocked waiting to complete, the call was interrupted by a signal handler; see fcntl(2) and signal(7).

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 the file descriptor, fd:

EBADF

fd is not a valid descriptor.

EBADF or EINVAL

fd is not open for writing.

EINVAL

fd does not reference a regular file.

CONFORMING TO

4.4BSD, SVr4, POSIX.1-2001 (these calls first appeared in 4.2BSD).

NOTES

The details in DESCRIPTION are for XSI-compliant systems. For non-XSI-compliant systems, the POSIX standard allows two behaviors 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 nonnative 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.

The original Linux truncate() and ftruncate() system calls were not designed to handle large file offsets. Consequently, Linux 2.4 added truncate64() and ftruncate64() system calls that handle large files. However, these details can be ignored by applications using glibc, whose wrapper functions transparently employ the more recent system calls where they are available.

On some 32-bit architectures, the calling signature for these system calls differ, for the reasons described in syscall(2).

BUGS

A header file bug in glibc 2.12 meant that the minimum value of _POSIX_C_SOURCE required to expose the declaration of ftruncate() was 200809L instead of 200112L. This has been fixed in later glibc versions.

SEE ALSO

open(2), stat(2), path_resolution(7)

COLOPHON

This page is part of release 3.52 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man−pages/.


  Copyright (c) 1983, 1991 The Regents of the University of California.
All rights reserved.

%%%LICENSE_START(BSD_4_CLAUSE_UCB)
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
OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
SUCH DAMAGE.
%%%LICENSE_END

    (#)truncate.2 6.9 (Berkeley) 3/10/91

Modified 1993-07-24 by Rik Faith <faithcs.unc.edu>
Modified 1996-10-22 by Eric S. Raymond <esrthyrsus.com>
Modified 1998-12-21 by Andries Brouwer <aebcwi.nl>
Modified 2002-01-07 by Michael Kerrisk <mtk.manpagesgmail.com>
Modified 2002-04-06 by Andries Brouwer <aebcwi.nl>
Modified 2004-06-23 by Michael Kerrisk <mtk.manpagesgmail.com>