mirror of https://github.com/mkerrisk/man-pages
215 lines
6.2 KiB
Groff
215 lines
6.2 KiB
Groff
.\" Copyright (c) 1983, 1991 The Regents of the University of California.
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)truncate.2 6.9 (Berkeley) 3/10/91
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.\"
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.\" Modified 1993-07-24 by Rik Faith <faith@cs.unc.edu>
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.\" Modified 1996-10-22 by Eric S. Raymond <esr@thyrsus.com>
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.\" Modified 1998-12-21 by Andries Brouwer <aeb@cwi.nl>
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.\" Modified 2002-01-07 by Michael Kerrisk <mtk.manpages@gmail.com>
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.\" Modified 2002-04-06 by Andries Brouwer <aeb@cwi.nl>
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.\" Modified 2004-06-23 by Michael Kerrisk <mtk.manpages@gmail.com>
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.\"
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.TH TRUNCATE 2 2007-07-26 "Linux" "Linux Programmer's Manual"
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.SH NAME
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truncate, ftruncate \- truncate a file to a specified length
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.SH SYNOPSIS
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.B #include <unistd.h>
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.br
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.B #include <sys/types.h>
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.sp
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.BI "int truncate(const char *" path ", off_t " length );
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.br
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.BI "int ftruncate(int " fd ", off_t " length );
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.sp
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.in -4n
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Feature Test Macro Requirements for glibc (see
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.BR feature_test_macros (7)):
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.in
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.ad l
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.sp
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.BR getdtablesize ():
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_BSD_SOURCE || _XOPEN_SOURCE\ >=\ 500 || _POSIX_C_SOURCE\ >=\ 200112L
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.ad b
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.SH DESCRIPTION
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The
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.BR truncate ()
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and
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.BR ftruncate ()
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functions cause the regular file named by
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.I path
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or referenced by
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.I fd
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to be truncated to a size of precisely
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.I length
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bytes.
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.LP
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If the file previously was larger than this size, the extra data is lost.
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If the file previously was shorter, it is extended, and
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the extended part reads as null bytes ('\\0').
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.LP
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The file offset is not changed.
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.LP
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If the size changed, then the st_ctime and st_mtime fields
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(respectively, time of last status change and
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time of last modification; see
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.BR stat (2))
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for the file are updated,
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and the set-user-ID and set-group-ID permission bits may be cleared.
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.LP
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With
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.BR ftruncate (),
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the file must be open for writing; with
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.BR truncate (),
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the file must be writable.
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.SH "RETURN VALUE"
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On success, zero is returned.
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On error, \-1 is returned, and
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.I errno
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is set appropriately.
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.SH ERRORS
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For
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.BR truncate ():
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.TP
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.B EACCES
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Search permission is denied for a component of the path prefix,
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or the named file is not writable by the user.
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(See also
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.BR path_resolution (7).)
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.TP
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.B EFAULT
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.I Path
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points outside the process's allocated address space.
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.TP
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.B EFBIG
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The argument
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.I length
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is larger than the maximum file size. (XSI)
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.TP
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.B EINTR
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A signal was caught during execution.
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.TP
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.B EINVAL
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The argument
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.I length
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is negative or larger than the maximum file size.
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.TP
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.B EIO
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An I/O error occurred updating the inode.
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.TP
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.B EISDIR
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The named file is a directory.
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.TP
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.B ELOOP
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Too many symbolic links were encountered in translating the pathname.
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.TP
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.B ENAMETOOLONG
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A component of a pathname exceeded 255 characters,
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or an entire pathname exceeded 1023 characters.
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.TP
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.B ENOENT
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The named file does not exist.
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.TP
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.B ENOTDIR
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A component of the path prefix is not a directory.
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.TP
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.B EPERM
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.\" This happens for at leas MSDOS and VFAT fil systems
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.\" on kernel 2.6.13
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The underlying file system does not support extending
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a file beyond its current size.
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.TP
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.B EROFS
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The named file resides on a read-only file system.
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.TP
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.B ETXTBSY
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The file is a pure procedure (shared text) file that is being executed.
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.PP
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For
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.BR ftruncate ()
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the same errors apply, but instead of things that can be wrong with
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.IR path ,
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we now have things that can be wrong with
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.IR fd :
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.TP
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.B EBADF
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The
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.I fd
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is not a valid descriptor.
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.TP
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.BR EBADF " or " EINVAL
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The
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.I fd
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is not open for writing.
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.TP
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.B EINVAL
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The
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.I fd
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does not reference a regular file.
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.SH "CONFORMING TO"
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4.4BSD, SVr4, POSIX.1-2001 (these calls first appeared in 4.2BSD).
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.\" POSIX.1-1996 has
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.\" .BR ftruncate ().
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.\" POSIX.1-2001 also has
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.\" .BR truncate (),
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.\" as an XSI extension.
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.\" .LP
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.\" SVr4 documents additional
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.\" .BR truncate ()
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.\" error conditions EMFILE, EMULTIHP, ENFILE, ENOLINK. SVr4 documents for
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.\" .BR ftruncate ()
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.\" an additional EAGAIN error condition.
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.SH NOTES
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The above description is for XSI-compliant systems.
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For non-XSI-compliant systems, the POSIX standard allows
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two behaviors for
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.BR ftruncate ()
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when
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.I length
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exceeds the file length
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(note that
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.BR truncate ()
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is not specified at all in such an environment):
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either returning an error, or extending the file.
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Like most Unix implementations, Linux follows the XSI requirement
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when dealing with native file systems.
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However, some non-native file systems do not permit
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.BR truncate ()
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and
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.BR ftruncate ()
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to be used to extend a file beyond its current length:
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a notable example on Linux is VFAT.
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.\" At the very least: OSF/1, Solaris 7, and FreeBSD conform, mtk, Jan 2002
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.SH "SEE ALSO"
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.BR open (2),
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.BR stat (2),
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.BR path_resolution (7)
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