1.\" $OpenBSD: truncate.2,v 1.21 2022/05/23 15:17:11 millert 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 23 2022 $ 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.In 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 62.Rv -std 63.Sh ERRORS 64.Fn truncate 65and 66.Fn ftruncate 67will fail if: 68.Bl -tag -width Er 69.It Bq Er EINVAL 70The 71.Fa length 72is a negative value. 73.It Bq Er EFBIG 74The 75.Fa length 76exceeds the process's file size limit or the maximum file size 77of the underlying filesystem. 78.It Bq Er EIO 79An I/O error occurred updating the inode. 80.El 81.Pp 82In addition, 83.Fn truncate 84may return the following errors: 85.Bl -tag -width Er 86.It Bq Er ENOTDIR 87A component of the path prefix is not a directory. 88.It Bq Er ENAMETOOLONG 89A component of a pathname exceeded 90.Dv NAME_MAX 91characters, or an entire pathname (including the terminating NUL) 92exceeded 93.Dv PATH_MAX 94bytes. 95.It Bq Er ENOENT 96The named file does not exist. 97.It Bq Er EACCES 98Search permission is denied for a component of the path prefix. 99.It Bq Er EACCES 100The named file is not writable by the user. 101.It Bq Er ELOOP 102Too many symbolic links were encountered in translating the pathname. 103.It Bq Er EISDIR 104The named file is a directory. 105.It Bq Er EROFS 106The named file resides on a read-only file system. 107.It Bq Er ETXTBSY 108The file is a pure procedure (shared text) file that is being executed. 109.It Bq Er EFAULT 110.Fa path 111points outside the process's allocated address space. 112.El 113.Pp 114.Fn ftruncate 115may return the following errors: 116.Bl -tag -width Er 117.It Bq Er EBADF 118The 119.Fa fd 120is not a valid descriptor. 121.It Bq Er EINVAL 122The 123.Fa fd 124references a socket, not a file. 125.It Bq Er EINVAL 126The 127.Fa fd 128is not open for writing. 129.El 130.Sh SEE ALSO 131.Xr open 2 132.Sh STANDARDS 133The 134.Fn truncate 135and 136.Fn ftruncate 137functions conform to 138.St -p1003.1-2008 . 139.Sh HISTORY 140The 141.Fn truncate 142and 143.Fn ftruncate 144system calls first appeared in 145.Bx 4.1c . 146.Sh BUGS 147These calls should be generalized to allow ranges of bytes in a file 148to be discarded. 149.Pp 150Use of 151.Fn truncate 152to extend a file is not portable. 153