[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 ftruncate
and
.Fn truncate
cause 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 size exceeds 
.Fa length ,
any extra data is discarded. If the file size is smaller than 
.Fa length , 
the file is extended and filled with zeros to the indicated length.
The
.Fn ftruncate
form requires the file to be open for writing.
.Pp
Note: 
.Fn ftruncate 
and
.Fn truncate
do not modify the current file offset for any open file descriptions associated with the file.
.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	55	.Sh DESCRIPTION
b0d623f7 A	56	.Fn ftruncate
	57	and
	58	.Fn truncate
	59	cause the file named by
	60	.Fa path ,
9bccf70c	61	or referenced by
b0d623f7 A	62	.Fa fildes ,
b0d623f7 A	63	to be truncated (or extended) to
9bccf70c	64	.Fa length
b0d623f7 A	65	bytes in size. If the file size exceeds
	66	.Fa length ,
	67	any extra data is discarded. If the file size is smaller than
	68	.Fa length ,
	69	the file is extended and filled with zeros to the indicated length.
	70	The
	71	.Fn ftruncate
	72	form requires the file to be open for writing.
	73	.Pp
	74	Note:
	75	.Fn ftruncate
	76	and
	77	.Fn truncate
	78	do not modify the current file offset for any open file descriptions associated with the file.
9bccf70c A	79	.Sh RETURN VALUES
	80	A value of 0 is returned if the call succeeds. If the call
	81	fails a -1 is returned, and the global variable
	82	.Va errno
	83	specifies the error.
	84	.Sh ERRORS
2d21ac55 A	85	.Pp
	86	The
	87	.Fn ftruncate
	88	system call will fail if:
9bccf70c	89	.Bl -tag -width Er
2d21ac55 A	90	.\" ===========
	91	.It Bq Er EBADF
	92	.Fa fildes
	93	is not a valid descriptor open for writing.
	94	.\" ===========
	95	.It Bq Er EFBIG
	96	The file is a regular file and
	97	.Fa length
	98	is greater than the offset maximum established
	99	in the open file description associated with
	100	.Fa fildes .
	101	.\" ===========
	102	.It Bq Er EINVAL
	103	.Fa fildes
	104	references a socket, not a file.
	105	.\" ===========
	106	.It Bq Er EINVAL
	107	.Fa fildes
	108	is not open for writing.
	109	.\" ===========
	110	.It Bq Er EROFS
	111	The named file resides on a read-only file system.
	112	.El
	113	.Pp
	114	The
	115	.Fn truncate
	116	system call will fail if:
	117	.Bl -tag -width Er
	118	.\" ===========
9bccf70c A	119	.It Bq Er EACCES
9bccf70c A	120	Search permission is denied for a component of the path prefix.
2d21ac55	121	.\" ===========
9bccf70c A	122	.It Bq Er EACCES
9bccf70c A	123	The named file is not writable by the user.
2d21ac55 A	124	.\" ===========
	125	.It Bq Er EFAULT
	126	.Fa Path
	127	points outside the process's allocated address space.
	128	.\" ===========
9bccf70c A	129	.It Bq Er EISDIR
9bccf70c A	130	The named file is a directory.
2d21ac55 A	131	.\" ===========
	132	.It Bq Er ELOOP
	133	Too many symbolic links are encountered in translating the pathname.
	134	This is taken to be indicative of a looping symbolic link.
	135	.\" ===========
	136	.It Bq Er ENAMETOOLONG
	137	A component of a pathname exceeds
	138	.Dv {NAME_MAX}
	139	characters, or an entire path name exceeds
	140	.Dv {PATH_MAX}
	141	characters.
	142	.\" ===========
	143	.It Bq Er ENOENT
	144	The named file does not exist.
	145	.\" ===========
	146	.It Bq Er ENOTDIR
	147	A component of the path prefix is not a directory.
	148	.\" ===========
9bccf70c A	149	.It Bq Er EROFS
9bccf70c A	150	The named file resides on a read-only file system.
2d21ac55	151	.\" ===========
9bccf70c A	152	.It Bq Er ETXTBSY
9bccf70c A	153	The file is a pure procedure (shared text) file that is being executed.
9bccf70c A	154	.El
9bccf70c A	155	.Pp
9bccf70c	156	The
2d21ac55 A	157	.Fn ftruncate
	158	and
	159	.Fn truncate
	160	system calls will fail if:
	161	.Bl -tag -width Er
	162	.\" ===========
	163	.It Bq Er EFBIG
	164	The length argument was greater than the maximum file size.
	165	.\" ===========
	166	.It Bq Er EINTR
	167	A signal is caught during execution.
	168	.\" ===========
9bccf70c A	169	.It Bq Er EINVAL
9bccf70c A	170	The
2d21ac55 A	171	.Fa length
	172	argument is less than 0.
	173	.\" ===========
	174	.It Bq Er EIO
	175	An I/O error occurred while reading from or writing to a file system.
9bccf70c A	176	.El
	177	.Sh SEE ALSO
	178	.Xr open 2
	179	.Sh BUGS
	180	These calls should be generalized to allow ranges
	181	of bytes in a file to be discarded.
	182	.Pp
	183	Use of
	184	.Fn truncate
	185	to extend a file is not portable.
	186	.Sh HISTORY
	187	The
	188	.Fn truncate
	189	and
	190	.Fn ftruncate
	191	function calls appeared in
	192	.Bx 4.2 .