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.\" 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
.\" 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.
.\"
.\" @(#)truncate.2 6.9 (Berkeley) 3/10/91
.\"
.\" Modified Sat Jul 24 12:46:33 1993 by Rik Faith (faith@cs.unc.edu)
.\" Modified Tue Oct 22 22:36:33 1996 by Eric S. Raymond <esr@thyrsus.com>
.\" Modified Mon Dec 21 13:37:05 1998 by Andries Brouwer (aeb@cwi.nl)
.\"
.TH TRUNCATE 2 "21 December 1998" "" "Linux Programmer's Manual"
.SH NAME
truncate, ftruncate \- truncate a file to a specified length
.SH SYNOPSIS
.B #include <unistd.h>
.sp
.BI "int truncate(const char *" path ", off_t " length );
.br
.BI "int ftruncate(int " fd ", off_t " length );
.SH DESCRIPTION
.B Truncate
causes the file named by
.I path
or referenced by
.I fd
to be truncated to at most
.I length
bytes in size.
If the file previously was larger than this size, the extra data is lost.
If the file previously was shorter, it is unspecified whether the file
is left unchanged or is extended. In the latter case the extended part
reads as zero bytes.
With
.BR ftruncate ,
the file must be open for writing.
.SH "RETURN VALUE"
On success, zero is returned. On error, \-1 is returned, and
.I errno
is set appropriately.
.SH ERRORS
For
.BR truncate :
.TP
.B ENOTDIR
A component of the path prefix is not a directory.
.TP
.B EINVAL
The pathname contains a character with the high-order bit set.
.TP
.B ENAMETOOLONG
A component of a pathname exceeded 255 characters,
or an entire path name exceeded 1023 characters.
.TP
.B ENOENT
The named file does not exist.
.TP
.B EACCES
Search permission is denied for a component of the path prefix.
.TP
.B EACCES
The named file is not writable by the user.
.TP
.B ELOOP
Too many symbolic links were encountered in translating the pathname.
.TP
.B EISDIR
The named file is a directory.
.TP
.B EROFS
The named file resides on a read-only file system.
.TP
.B ETXTBSY
The file is a pure procedure (shared text) file that is being executed.
.TP
.B EIO
An I/O error occurred updating the inode.
.TP
.B EFAULT
.I Path
points outside the process's allocated address space.
.PP
For
.BR ftruncate :
.TP
.B EBADF
The
.I fd
is not a valid descriptor.
.TP
.B EINVAL
The
.I fd
references a socket, not a file.
.TP
.B EINVAL
The
.I fd
is not open for writing.
.SH "CONFORMING TO"
4.4BSD, SVr4 (these function calls first appeared in BSD 4.2).
SVr4 documents additional
.B truncate
error conditions EINTR, EMFILE, EMULTIHP, ENAMETOOLONG, ENFILE,
ENOLINK, ENOTDIR. SVr4 documents for
.B ftruncate
additional EAGAIN and EINTR error conditions.
POSIX has
.I ftruncate
but not
.IR truncate .
.PP
The POSIX standard does not define what happens if the file has fewer bytes
than
.IR length .
.SH BUGS
These calls should be generalized to allow ranges of bytes in a file to be
discarded.
.SH "SEE ALSO"
.BR open (2)
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