.\"	$NetBSD: truncate.2,v 1.7 1995/02/27 12:39:00 cgd Exp $
.\"
.\" Copyright (c) 1983, 1991, 1993
.\"	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	8.1 (Berkeley) 6/4/93
.\"
.Dd June 4, 1993
.Dt TRUNCATE 2
.Os BSD 4.2
.Sh NAME
.Nm ftruncate ,
.Nm truncate
.Nd truncate or extend a file to a specified length
.Sh SYNOPSIS
.Fd #include <unistd.h>
.Ft int
.Fo ftruncate
.Fa "int fildes"
.Fa "off_t length"
.Fc
.Ft int
.Fo truncate
.Fa "const char *path"
.Fa "off_t length"
.Fc
.Sh DESCRIPTION
.Fn Truncate
causes the file named by
.Fa path
or referenced by
.Fa fildes
to be truncated or extended to
.Fa length
bytes in size.  If the file previously
was larger than this size, the extra data
is lost. If the file was smaller than this size, it will be extended as
if by writing bytes with the value zero.
With
.Fn ftruncate ,
the file must be open for writing.
.Sh RETURN VALUES
A value of 0 is returned if the call succeeds.  If the call
fails a -1 is returned, and the global variable
.Va errno
specifies the error.
.Sh ERRORS
.Pp
The
.Fn ftruncate
system call will fail if:
.Bl -tag -width Er
.\" ===========
.It Bq Er EBADF
.Fa fildes
is not a valid descriptor open for writing.
.\" ===========
.It Bq Er EFBIG
The file is a regular file and
.Fa length
is greater than the offset maximum established
in the open file description associated with
.Fa fildes .
.\" ===========
.It Bq Er EINVAL
.Fa fildes
references a socket, not a file.
.\" ===========
.It Bq Er EINVAL
.Fa fildes
is not open for writing.
.\" ===========
.It Bq Er EROFS
The named file resides on a read-only file system.
.El
.Pp
The
.Fn truncate
system call will fail if:
.Bl -tag -width Er
.\" ===========
.It Bq Er EACCES
Search permission is denied for a component of the path prefix.
.\" ===========
.It Bq Er EACCES
The named file is not writable by the user.
.\" ===========
.It Bq Er EFAULT
.Fa Path
points outside the process's allocated address space.
.\" ===========
.It Bq Er EISDIR
The named file is a directory.
.\" ===========
.It Bq Er ELOOP
Too many symbolic links are encountered in translating the pathname.
This is taken to be indicative of a looping symbolic link.
.\" ===========
.It Bq Er ENAMETOOLONG
A component of a pathname exceeds
.Dv {NAME_MAX}
characters, or an entire path name exceeds 
.Dv {PATH_MAX}
characters.
.\" ===========
.It Bq Er ENOENT
The named file does not exist.
.\" ===========
.It Bq Er ENOTDIR
A component of the path prefix is not a directory.
.\" ===========
.It Bq Er EROFS
The named file resides on a read-only file system.
.\" ===========
.It Bq Er ETXTBSY
The file is a pure procedure (shared text) file that is being executed.
.El
.Pp
The
.Fn ftruncate
and
.Fn truncate
system calls will fail if:
.Bl -tag -width Er
.\" ===========
.It Bq Er EFBIG
The length argument was greater than the maximum file size.
.\" ===========
.It Bq Er EINTR
A signal is caught during execution.
.\" ===========
.It Bq Er EINVAL
The
.Fa length
argument is less than 0.
.\" ===========
.It Bq Er EIO
An I/O error occurred while reading from or writing to a file system.
.El
.Sh SEE ALSO
.Xr open 2
.Sh BUGS
These calls should be generalized to allow ranges
of bytes in a file to be discarded.
.Pp
Use of
.Fn truncate
to extend a file is not portable.
.Sh HISTORY
The
.Fn truncate
and
.Fn ftruncate
function calls appeared in
.Bx 4.2 .