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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.\" 30.Dd March 30, 2020 31.Dt TRUNCATE 2 32.Os 33.Sh NAME 34.Nm truncate , 35.Nm ftruncate 36.Nd truncate or extend a file to a specified length 37.Sh LIBRARY 38.Lb libc 39.Sh SYNOPSIS 40.In unistd.h 41.Ft int 42.Fn truncate "const char *path" "off_t length" 43.Ft int 44.Fn ftruncate "int fd" "off_t length" 45.Sh DESCRIPTION 46The 47.Fn truncate 48system call 49causes the file named by 50.Fa path 51or referenced by 52.Fa fd 53to be truncated or extended to 54.Fa length 55bytes in size. 56If the file 57was larger than this size, the extra data 58is lost. 59If the file was smaller than this size, 60it will be extended as if by writing bytes 61with the value zero. 62.Pp 63The 64.Fn ftruncate 65system call causes the file or shared memory object backing the file descriptor 66.Fa fd 67to be truncated or extended to 68.Fa length 69bytes in size. 70The file descriptor must be a valid file descriptor open for writing. 71The file position pointer associated with the file descriptor 72.Fa fd 73will not be modified. 74.Sh RETURN VALUES 75.Rv -std 76If the file to be modified is not a directory or 77a regular file, the 78.Fn truncate 79call has no effect and returns the value 0. 80.Sh ERRORS 81The 82.Fn truncate 83system call 84succeeds unless: 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 255 characters, 90or an entire path name exceeded 1023 characters. 91.It Bq Er ENOENT 92The named file does not exist. 93.It Bq Er EACCES 94Search permission is denied for a component of the path prefix. 95.It Bq Er EACCES 96The named file is not writable by the user. 97.It Bq Er ELOOP 98Too many symbolic links were encountered in translating the pathname. 99.It Bq Er EPERM 100The named file has its immutable or append-only flag set, see the 101.Xr chflags 2 102manual page for more information. 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 EFBIG 110The 111.Fa length 112argument was greater than the maximum file size. 113.It Bq Er EINVAL 114The 115.Fa length 116argument was less than 0. 117.It Bq Er EIO 118An I/O error occurred updating the inode. 119.It Bq Er EINTEGRITY 120Corrupted data was detected while reading from the file system. 121.It Bq Er EFAULT 122The 123.Fa path 124argument 125points outside the process's allocated address space. 126.El 127.Pp 128The 129.Fn ftruncate 130system call 131succeeds unless: 132.Bl -tag -width Er 133.It Bq Er EBADF 134The 135.Fa fd 136argument 137is not a valid descriptor. 138.It Bq Er EINVAL 139The 140.Fa fd 141argument 142references a file descriptor that is not a regular file or shared memory object. 143.It Bq Er EINVAL 144The 145.Fa fd 146descriptor 147is not open for writing. 148.El 149.Sh SEE ALSO 150.Xr chflags 2 , 151.Xr open 2 , 152.Xr shm_open 2 153.Sh HISTORY 154The 155.Fn truncate 156and 157.Fn ftruncate 158system calls appeared in 159.Bx 4.2 . 160.Sh BUGS 161These calls should be generalized to allow ranges 162of bytes in a file to be discarded. 163.Pp 164Historically, the use of 165.Fn truncate 166or 167.Fn ftruncate 168to extend a file was not portable, but this behavior became required in 169.St -p1003.1-2008 . 170