1.\" $OpenBSD: truncate.2,v 1.13 2007/05/31 19:19:34 jmc Exp $ 2.\" $NetBSD: truncate.2,v 1.7 1995/02/27 12:39:00 cgd Exp $ 3.\" 4.\" Copyright (c) 1983, 1991, 1993 5.\" The Regents of the University of California. All rights reserved. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in the 14.\" documentation and/or other materials provided with the distribution. 15.\" 3. Neither the name of the University nor the names of its contributors 16.\" may be used to endorse or promote products derived from this software 17.\" without specific prior written permission. 18.\" 19.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 20.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 23.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29.\" SUCH DAMAGE. 30.\" 31.\" @(#)truncate.2 8.1 (Berkeley) 6/4/93 32.\" 33.Dd $Mdocdate: May 31 2007 $ 34.Dt TRUNCATE 2 35.Os 36.Sh NAME 37.Nm truncate , 38.Nm ftruncate 39.Nd truncate or extend a file to a specified length 40.Sh SYNOPSIS 41.Fd #include <unistd.h> 42.Ft int 43.Fn truncate "const char *path" "off_t length" 44.Ft int 45.Fn ftruncate "int fd" "off_t length" 46.Sh DESCRIPTION 47.Fn truncate 48causes the file named by 49.Fa path 50or referenced by 51.Fa fd 52to be truncated or extended to 53.Fa length 54bytes in size. 55If the file was larger than this size, the extra data is lost. 56If the file was smaller than this size, it will be extended as if by 57writing bytes with the value zero. 58With 59.Fn ftruncate , 60the file must be open for writing. 61.Sh RETURN VALUES 62A value of 0 is returned if the call succeeds. 63If the call fails a \-1 is returned, and the global variable 64.Va errno 65specifies the error. 66.Sh ERRORS 67.Fn truncate 68succeeds unless: 69.Bl -tag -width Er 70.It Bq Er ENOTDIR 71A component of the path prefix is not a directory. 72.It Bq Er ENAMETOOLONG 73A component of a pathname exceeded 74.Dv {NAME_MAX} 75characters, or an entire path name exceeded 76.Dv {PATH_MAX} 77characters. 78.It Bq Er ENOENT 79The named file does not exist. 80.It Bq Er EACCES 81Search permission is denied for a component of the path prefix. 82.It Bq Er EACCES 83The named file is not writable by the user. 84.It Bq Er ELOOP 85Too many symbolic links were encountered in translating the pathname. 86.It Bq Er EISDIR 87The named file is a directory. 88.It Bq Er EROFS 89The named file resides on a read-only file system. 90.It Bq Er ETXTBSY 91The file is a pure procedure (shared text) file that is being executed. 92.It Bq Er EIO 93An I/O error occurred updating the inode. 94.It Bq Er EFAULT 95.Fa path 96points outside the process's allocated address space. 97.It Bq Er EPERM 98The effective user ID does not match the owner of the file and 99the effective user ID is not the superuser. 100.El 101.Pp 102.Fn ftruncate 103succeeds unless: 104.Bl -tag -width Er 105.It Bq Er EBADF 106The 107.Fa fd 108is not a valid descriptor. 109.It Bq Er EINVAL 110The 111.Fa fd 112references a socket, not a file. 113.It Bq Er EINVAL 114The 115.Fa fd 116is not open for writing. 117.It Bq Er EINVAL 118The 119.Fa length 120is a negative value. 121.El 122.Sh SEE ALSO 123.Xr open 2 124.Sh HISTORY 125The 126.Fn truncate 127and 128.Fn ftruncate 129function calls appeared in 130.Bx 4.2 . 131.Sh BUGS 132These calls should be generalized to allow ranges of bytes in a file 133to be discarded. 134.Pp 135Use of 136.Fn truncate 137to extend a file is not portable. 138