1.\" Copyright (c) 1983, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. All advertising materials mentioning features or use of this software 13.\" must display the following acknowledgement: 14.\" This product includes software developed by the University of 15.\" California, Berkeley and its contributors. 16.\" 4. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" @(#)truncate.2 8.1 (Berkeley) 6/4/93 33.\" $FreeBSD$ 34.\" 35.Dd June 4, 1993 36.Dt TRUNCATE 2 37.Os 38.Sh NAME 39.Nm truncate , 40.Nm ftruncate 41.Nd truncate or extend a file to a specified length 42.Sh LIBRARY 43.Lb libc 44.Sh SYNOPSIS 45.In unistd.h 46.Ft int 47.Fn truncate "const char *path" "off_t length" 48.Ft int 49.Fn ftruncate "int fd" "off_t length" 50.Sh DESCRIPTION 51The 52.Fn truncate 53system call 54causes the file named by 55.Fa path 56or referenced by 57.Fa fd 58to be truncated or extended to 59.Fa length 60bytes in size. 61If the file 62was larger than this size, the extra data 63is lost. 64If the file was smaller than this size, 65it will be extended as if by writing bytes 66with the value zero. 67With 68.Fn ftruncate , 69the file must be open for writing. 70.Sh RETURN VALUES 71.Rv -std 72.Sh ERRORS 73The 74.Fn truncate 75system call 76succeeds unless: 77.Bl -tag -width Er 78.It Bq Er ENOTDIR 79A component of the path prefix is not a directory. 80.It Bq Er ENAMETOOLONG 81A component of a pathname exceeded 255 characters, 82or an entire path name exceeded 1023 characters. 83.It Bq Er ENOENT 84The named file does not exist. 85.It Bq Er EACCES 86Search permission is denied for a component of the path prefix. 87.It Bq Er EACCES 88The named file is not writable by the user. 89.It Bq Er ELOOP 90Too many symbolic links were encountered in translating the pathname. 91.It Bq Er EISDIR 92The named file is a directory. 93.It Bq Er EROFS 94The named file resides on a read-only file system. 95.It Bq Er ETXTBSY 96The file is a pure procedure (shared text) file that is being executed. 97.It Bq Er EIO 98An I/O error occurred updating the inode. 99.It Bq Er EFAULT 100The 101.Fa path 102argument 103points outside the process's allocated address space. 104.El 105.Pp 106The 107.Fn ftruncate 108system call 109succeeds unless: 110.Bl -tag -width Er 111.It Bq Er EBADF 112The 113.Fa fd 114argument 115is not a valid descriptor. 116.It Bq Er EINVAL 117The 118.Fa fd 119argument 120references a socket, not a file. 121.It Bq Er EINVAL 122The 123.Fa fd 124descriptor 125is not open for writing. 126.El 127.Sh SEE ALSO 128.Xr open 2 129.Sh BUGS 130These calls should be generalized to allow ranges 131of bytes in a file to be discarded. 132.Pp 133Use of 134.Fn truncate 135to extend a file is not portable. 136.Sh HISTORY 137The 138.Fn truncate 139system call appeared in 140.Bx 4.2 . 141