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. Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.\" @(#)truncate.2 8.1 (Berkeley) 6/4/93 29.\" $FreeBSD$ 30.\" 31.Dd May 4, 2015 32.Dt TRUNCATE 2 33.Os 34.Sh NAME 35.Nm truncate , 36.Nm ftruncate 37.Nd truncate or extend a file to a specified length 38.Sh LIBRARY 39.Lb libc 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 47The 48.Fn truncate 49system call 50causes the file named by 51.Fa path 52or referenced by 53.Fa fd 54to be truncated or extended to 55.Fa length 56bytes in size. 57If the file 58was larger than this size, the extra data 59is lost. 60If the file was smaller than this size, 61it will be extended as if by writing bytes 62with the value zero. 63.Pp 64The 65.Fn ftruncate 66system call causes the file or shared memory object backing the file descriptor 67.Fa fd 68to be truncated or extended to 69.Fa length 70bytes in size. 71The file descriptor must be a valid file descriptor open for writing. 72The file position pointer associated with the file descriptor 73.Fa fd 74will not be modified. 75.Sh RETURN VALUES 76.Rv -std 77If the file to be modified is not a directory or 78a regular file, the 79.Fn truncate 80call has no effect and returns the value 0. 81.Sh ERRORS 82The 83.Fn truncate 84system call 85succeeds unless: 86.Bl -tag -width Er 87.It Bq Er ENOTDIR 88A component of the path prefix is not a directory. 89.It Bq Er ENAMETOOLONG 90A component of a pathname exceeded 255 characters, 91or an entire path name exceeded 1023 characters. 92.It Bq Er ENOENT 93The named file does not exist. 94.It Bq Er EACCES 95Search permission is denied for a component of the path prefix. 96.It Bq Er EACCES 97The named file is not writable by the user. 98.It Bq Er ELOOP 99Too many symbolic links were encountered in translating the pathname. 100.It Bq Er EPERM 101The named file has its immutable or append-only flag set, see the 102.Xr chflags 2 103manual page for more information. 104.It Bq Er EISDIR 105The named file is a directory. 106.It Bq Er EROFS 107The named file resides on a read-only file system. 108.It Bq Er ETXTBSY 109The file is a pure procedure (shared text) file that is being executed. 110.It Bq Er EFBIG 111The 112.Fa length 113argument was greater than the maximum file size. 114.It Bq Er EINVAL 115The 116.Fa length 117argument was less than 0. 118.It Bq Er EIO 119An I/O error occurred updating the inode. 120.It Bq Er EFAULT 121The 122.Fa path 123argument 124points outside the process's allocated address space. 125.El 126.Pp 127The 128.Fn ftruncate 129system call 130succeeds unless: 131.Bl -tag -width Er 132.It Bq Er EBADF 133The 134.Fa fd 135argument 136is not a valid descriptor. 137.It Bq Er EINVAL 138The 139.Fa fd 140argument 141references a file descriptor that is not a regular file or shared memory object. 142.It Bq Er EINVAL 143The 144.Fa fd 145descriptor 146is not open for writing. 147.El 148.Sh SEE ALSO 149.Xr chflags 2 , 150.Xr open 2 , 151.Xr shm_open 2 152.Sh HISTORY 153The 154.Fn truncate 155and 156.Fn ftruncate 157system calls appeared in 158.Bx 4.2 . 159.Sh BUGS 160These calls should be generalized to allow ranges 161of bytes in a file to be discarded. 162.Pp 163Use of 164.Fn truncate 165to extend a file is not portable. 166