[apple/xnu.git] / bsd / man / man2 / truncate.2

.\"	$NetBSD: truncate.2,v 1.7 1995/02/27 12:39:00 cgd Exp $
.\"
.\" Copyright (c) 1983, 1991, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"	This product includes software developed by the University of
.\"	California, Berkeley and its contributors.
.\" 4. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\"     @(#)truncate.2	8.1 (Berkeley) 6/4/93
.\"
.Dd June 4, 1993
.Dt TRUNCATE 2
.Os BSD 4.2
.Sh NAME
.Nm ftruncate ,
.Nm truncate
.Nd truncate or extend a file to a specified length
.Sh SYNOPSIS
.Fd #include <unistd.h>
.Ft int
.Fo ftruncate
.Fa "int fildes"
.Fa "off_t length"
.Fc
.Ft int
.Fo truncate
.Fa "const char *path"
.Fa "off_t length"
.Fc
.Sh DESCRIPTION
.Fn Truncate
causes the file named by
.Fa path
or referenced by
.Fa fildes
to be truncated or extended to
.Fa length
bytes in size.  If the file previously
was larger than this size, the extra data
is lost. If the file was smaller than this size, it will be extended as
if by writing bytes with the value zero.
With
.Fn ftruncate ,
the file must be open for writing.
.Sh RETURN VALUES
A value of 0 is returned if the call succeeds.  If the call
fails a -1 is returned, and the global variable
.Va errno
specifies the error.
.Sh ERRORS
.Pp
The
.Fn ftruncate
system call will fail if:
.Bl -tag -width Er
.\" ===========
.It Bq Er EBADF
.Fa fildes
is not a valid descriptor open for writing.
.\" ===========
.It Bq Er EFBIG
The file is a regular file and
.Fa length
is greater than the offset maximum established
in the open file description associated with
.Fa fildes .
.\" ===========
.It Bq Er EINVAL
.Fa fildes
references a socket, not a file.
.\" ===========
.It Bq Er EINVAL
.Fa fildes
is not open for writing.
.\" ===========
.It Bq Er EROFS
The named file resides on a read-only file system.
.El
.Pp
The
.Fn truncate
system call will fail if:
.Bl -tag -width Er
.\" ===========
.It Bq Er EACCES
Search permission is denied for a component of the path prefix.
.\" ===========
.It Bq Er EACCES
The named file is not writable by the user.
.\" ===========
.It Bq Er EFAULT
.Fa Path
points outside the process's allocated address space.
.\" ===========
.It Bq Er EISDIR
The named file is a directory.
.\" ===========
.It Bq Er ELOOP
Too many symbolic links are encountered in translating the pathname.
This is taken to be indicative of a looping symbolic link.
.\" ===========
.It Bq Er ENAMETOOLONG
A component of a pathname exceeds
.Dv {NAME_MAX}
characters, or an entire path name exceeds 
.Dv {PATH_MAX}
characters.
.\" ===========
.It Bq Er ENOENT
The named file does not exist.
.\" ===========
.It Bq Er ENOTDIR
A component of the path prefix is not a directory.
.\" ===========
.It Bq Er EROFS
The named file resides on a read-only file system.
.\" ===========
.It Bq Er ETXTBSY
The file is a pure procedure (shared text) file that is being executed.
.El
.Pp
The
.Fn ftruncate
and
.Fn truncate
system calls will fail if:
.Bl -tag -width Er
.\" ===========
.It Bq Er EFBIG
The length argument was greater than the maximum file size.
.\" ===========
.It Bq Er EINTR
A signal is caught during execution.
.\" ===========
.It Bq Er EINVAL
The
.Fa length
argument is less than 0.
.\" ===========
.It Bq Er EIO
An I/O error occurred while reading from or writing to a file system.
.El
.Sh SEE ALSO
.Xr open 2
.Sh BUGS
These calls should be generalized to allow ranges
of bytes in a file to be discarded.
.Pp
Use of
.Fn truncate
to extend a file is not portable.
.Sh HISTORY
The
.Fn truncate
and
.Fn ftruncate
function calls appeared in
.Bx 4.2 .
Commit	Line	Data
9bccf70c A	1	.\" $NetBSD: truncate.2,v 1.7 1995/02/27 12:39:00 cgd 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 BSD 4.2
	39	.Sh NAME
2d21ac55 A	40	.Nm ftruncate ,
2d21ac55 A	41	.Nm truncate
9bccf70c A	42	.Nd truncate or extend a file to a specified length
	43	.Sh SYNOPSIS
	44	.Fd #include <unistd.h>
	45	.Ft int
2d21ac55 A	46	.Fo ftruncate
	47	.Fa "int fildes"
	48	.Fa "off_t length"
	49	.Fc
9bccf70c	50	.Ft int
2d21ac55 A	51	.Fo truncate
	52	.Fa "const char *path"
	53	.Fa "off_t length"
	54	.Fc
9bccf70c A	55	.Sh DESCRIPTION
	56	.Fn Truncate
	57	causes the file named by
	58	.Fa path
	59	or referenced by
2d21ac55	60	.Fa fildes
9bccf70c A	61	to be truncated or extended to
	62	.Fa length
	63	bytes in size. If the file previously
	64	was larger than this size, the extra data
	65	is lost. If the file was smaller than this size, it will be extended as
	66	if by writing bytes with the value zero.
	67	With
	68	.Fn ftruncate ,
	69	the file must be open for writing.
	70	.Sh RETURN VALUES
	71	A value of 0 is returned if the call succeeds. If the call
	72	fails a -1 is returned, and the global variable
	73	.Va errno
	74	specifies the error.
	75	.Sh ERRORS
2d21ac55 A	76	.Pp
	77	The
	78	.Fn ftruncate
	79	system call will fail if:
9bccf70c	80	.Bl -tag -width Er
2d21ac55 A	81	.\" ===========
	82	.It Bq Er EBADF
	83	.Fa fildes
	84	is not a valid descriptor open for writing.
	85	.\" ===========
	86	.It Bq Er EFBIG
	87	The file is a regular file and
	88	.Fa length
	89	is greater than the offset maximum established
	90	in the open file description associated with
	91	.Fa fildes .
	92	.\" ===========
	93	.It Bq Er EINVAL
	94	.Fa fildes
	95	references a socket, not a file.
	96	.\" ===========
	97	.It Bq Er EINVAL
	98	.Fa fildes
	99	is not open for writing.
	100	.\" ===========
	101	.It Bq Er EROFS
	102	The named file resides on a read-only file system.
	103	.El
	104	.Pp
	105	The
	106	.Fn truncate
	107	system call will fail if:
	108	.Bl -tag -width Er
	109	.\" ===========
9bccf70c A	110	.It Bq Er EACCES
9bccf70c A	111	Search permission is denied for a component of the path prefix.
2d21ac55	112	.\" ===========
9bccf70c A	113	.It Bq Er EACCES
9bccf70c A	114	The named file is not writable by the user.
2d21ac55 A	115	.\" ===========
	116	.It Bq Er EFAULT
	117	.Fa Path
	118	points outside the process's allocated address space.
	119	.\" ===========
9bccf70c A	120	.It Bq Er EISDIR
9bccf70c A	121	The named file is a directory.
2d21ac55 A	122	.\" ===========
	123	.It Bq Er ELOOP
	124	Too many symbolic links are encountered in translating the pathname.
	125	This is taken to be indicative of a looping symbolic link.
	126	.\" ===========
	127	.It Bq Er ENAMETOOLONG
	128	A component of a pathname exceeds
	129	.Dv {NAME_MAX}
	130	characters, or an entire path name exceeds
	131	.Dv {PATH_MAX}
	132	characters.
	133	.\" ===========
	134	.It Bq Er ENOENT
	135	The named file does not exist.
	136	.\" ===========
	137	.It Bq Er ENOTDIR
	138	A component of the path prefix is not a directory.
	139	.\" ===========
9bccf70c A	140	.It Bq Er EROFS
9bccf70c A	141	The named file resides on a read-only file system.
2d21ac55	142	.\" ===========
9bccf70c A	143	.It Bq Er ETXTBSY
9bccf70c A	144	The file is a pure procedure (shared text) file that is being executed.
9bccf70c A	145	.El
9bccf70c A	146	.Pp
9bccf70c	147	The
2d21ac55 A	148	.Fn ftruncate
	149	and
	150	.Fn truncate
	151	system calls will fail if:
	152	.Bl -tag -width Er
	153	.\" ===========
	154	.It Bq Er EFBIG
	155	The length argument was greater than the maximum file size.
	156	.\" ===========
	157	.It Bq Er EINTR
	158	A signal is caught during execution.
	159	.\" ===========
9bccf70c A	160	.It Bq Er EINVAL
9bccf70c A	161	The
2d21ac55 A	162	.Fa length
	163	argument is less than 0.
	164	.\" ===========
	165	.It Bq Er EIO
	166	An I/O error occurred while reading from or writing to a file system.
9bccf70c A	167	.El
	168	.Sh SEE ALSO
	169	.Xr open 2
	170	.Sh BUGS
	171	These calls should be generalized to allow ranges
	172	of bytes in a file to be discarded.
	173	.Pp
	174	Use of
	175	.Fn truncate
	176	to extend a file is not portable.
	177	.Sh HISTORY
	178	The
	179	.Fn truncate
	180	and
	181	.Fn ftruncate
	182	function calls appeared in
	183	.Bx 4.2 .