1.\" $NetBSD: truncate.2,v 1.15 2002/02/08 01:28:23 ross Exp $ 2.\" 3.\" Copyright (c) 1983, 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. All advertising materials mentioning features or use of this software 15.\" must display the following acknowledgement: 16.\" This product includes software developed by the University of 17.\" California, Berkeley and its contributors. 18.\" 4. Neither the name of the University nor the names of its contributors 19.\" may be used to endorse or promote products derived from this software 20.\" without specific prior written permission. 21.\" 22.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32.\" SUCH DAMAGE. 33.\" 34.\" @(#)truncate.2 8.1 (Berkeley) 6/4/93 35.\" 36.Dd June 4, 1993 37.Dt TRUNCATE 2 38.Os 39.Sh NAME 40.Nm truncate , 41.Nm ftruncate 42.Nd truncate a file to a specified length 43.Sh LIBRARY 44.Lb libc 45.Sh SYNOPSIS 46.Fd #include \*[Lt]unistd.h\*[Gt] 47.Ft int 48.Fn truncate "const char *path" "off_t length" 49.Ft int 50.Fn ftruncate "int fd" "off_t length" 51.Sh DESCRIPTION 52.Fn truncate 53causes the file named by 54.Fa path 55or referenced by 56.Fa fd 57to have a size of 58.Fa length 59bytes. If the file previously 60was larger than this size, the extra data 61is discarded. If it was previously shorter than 62.Fa length , 63its size is increased to the specified value and 64the extended area appears as if it were zero-filled. 65.Pp 66With 67.Fn ftruncate , 68the file must be open for writing; for 69.Fn truncate , 70the process must have write permissions for the file. 71.Sh RETURN VALUES 72A value of 0 is returned if the call succeeds. If the call 73fails a -1 is returned, and the global variable 74.Va errno 75specifies the error. 76.Sh ERRORS 77.Fn truncate 78succeeds unless: 79.Bl -tag -width Er 80.It Bq Er ENOTDIR 81A component of the path prefix is not a directory. 82.It Bq Er ENAMETOOLONG 83A component of a pathname exceeded 84.Dv {NAME_MAX} 85characters, or an entire path name exceeded 86.Dv {PATH_MAX} 87characters. 88.It Bq Er ENOENT 89The named file does not exist. 90.It Bq Er EACCES 91Search permission is denied for a component of the path prefix, or 92the named file is not writable by the user. 93.It Bq Er ELOOP 94Too many symbolic links were encountered in translating the pathname. 95.It Bq Er EISDIR 96The named file is a directory. 97.It Bq Er EROFS 98The named file resides on a read-only file system. 99.It Bq Er ETXTBSY 100The file is a pure procedure (shared text) file that is being executed. 101.It Bq Er EIO 102An I/O error occurred updating the inode. 103.It Bq Er EFAULT 104.Fa path 105points outside the process's allocated address space. 106.El 107.Pp 108.Fn ftruncate 109succeeds unless: 110.Bl -tag -width Er 111.It Bq Er EBADF 112The 113.Fa fd 114is not a valid descriptor. 115.It Bq Er EINVAL 116The 117.Fa fd 118references a socket, not a file, or 119the 120.Fa fd 121is not open for writing. 122.El 123.Sh SEE ALSO 124.Xr open 2 125.Sh HISTORY 126The 127.Fn truncate 128and 129.Fn ftruncate 130function calls appeared in 131.Bx 4.2 . 132.Sh BUGS 133These calls should be generalized to allow ranges 134of bytes in a file to be discarded. 135