1994-05-27 05:00:24 +00:00
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.\" Copyright (c) 1980, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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2017-02-28 23:42:47 +00:00
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.\" 3. Neither the name of the University nor the names of its contributors
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1994-05-27 05:00:24 +00:00
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)write.2 8.5 (Berkeley) 4/2/94
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1999-08-28 00:22:10 +00:00
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.\" $FreeBSD$
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1994-05-27 05:00:24 +00:00
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.\"
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2022-10-08 10:23:51 +00:00
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.Dd February 11, 2021
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1994-05-27 05:00:24 +00:00
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.Dt WRITE 2
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2001-07-10 13:41:46 +00:00
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.Os
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1994-05-27 05:00:24 +00:00
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.Sh NAME
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.Nm write ,
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1999-04-11 21:14:40 +00:00
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.Nm writev ,
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2006-04-14 19:34:07 +00:00
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.Nm pwrite ,
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.Nm pwritev
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1994-05-27 05:00:24 +00:00
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.Nd write output
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2000-04-21 09:42:15 +00:00
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.Sh LIBRARY
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.Lb libc
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1994-05-27 05:00:24 +00:00
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.Sh SYNOPSIS
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2001-10-01 16:09:29 +00:00
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.In unistd.h
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1994-05-27 05:00:24 +00:00
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.Ft ssize_t
|
2013-09-12 00:53:38 +00:00
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.Fn write "int fd" "const void *buf" "size_t nbytes"
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1994-05-27 05:00:24 +00:00
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.Ft ssize_t
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2013-09-12 00:53:38 +00:00
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.Fn pwrite "int fd" "const void *buf" "size_t nbytes" "off_t offset"
|
2012-01-22 11:15:48 +00:00
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.In sys/uio.h
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2005-07-07 18:17:55 +00:00
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.Ft ssize_t
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2013-09-12 00:53:38 +00:00
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.Fn writev "int fd" "const struct iovec *iov" "int iovcnt"
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1999-04-11 21:14:40 +00:00
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.Ft ssize_t
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2013-09-12 00:53:38 +00:00
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.Fn pwritev "int fd" "const struct iovec *iov" "int iovcnt" "off_t offset"
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1994-05-27 05:00:24 +00:00
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.Sh DESCRIPTION
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2002-12-18 09:22:32 +00:00
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The
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.Fn write
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system call
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1994-05-27 05:00:24 +00:00
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attempts to write
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.Fa nbytes
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of data to the object referenced by the descriptor
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2013-09-12 00:53:38 +00:00
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.Fa fd
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1994-05-27 05:00:24 +00:00
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from the buffer pointed to by
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.Fa buf .
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2002-12-18 09:22:32 +00:00
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The
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.Fn writev
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system call
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1994-05-27 05:00:24 +00:00
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performs the same action, but gathers the output data
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from the
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.Fa iovcnt
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buffers specified by the members of the
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.Fa iov
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array: iov[0], iov[1], ..., iov[iovcnt\|-\|1].
|
2002-12-18 09:22:32 +00:00
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The
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.Fn pwrite
|
2005-07-07 18:17:55 +00:00
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and
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.Fn pwritev
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system calls
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|
perform the same functions, but write to the specified position in
|
1999-04-11 21:14:40 +00:00
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the file without modifying the file pointer.
|
1994-05-27 05:00:24 +00:00
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.Pp
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For
|
2005-07-07 18:17:55 +00:00
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.Fn writev
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and
|
2006-10-21 20:36:50 +00:00
|
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.Fn pwritev ,
|
1994-05-27 05:00:24 +00:00
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the
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.Fa iovec
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structure is defined as:
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.Pp
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|
.Bd -literal -offset indent -compact
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struct iovec {
|
2003-01-12 15:18:47 +00:00
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|
void *iov_base; /* Base address. */
|
1997-01-30 22:39:40 +00:00
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size_t iov_len; /* Length. */
|
1994-05-27 05:00:24 +00:00
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};
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.Ed
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.Pp
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Each
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.Fa iovec
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entry specifies the base address and length of an area
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in memory from which data should be written.
|
2002-12-18 09:22:32 +00:00
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The
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.Fn writev
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system call
|
1994-05-27 05:00:24 +00:00
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will always write a complete area before proceeding
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to the next.
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.Pp
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On objects capable of seeking, the
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.Fn write
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starts at a position
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given by the pointer associated with
|
2013-09-12 00:53:38 +00:00
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.Fa fd ,
|
1994-05-27 05:00:24 +00:00
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see
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.Xr lseek 2 .
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Upon return from
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.Fn write ,
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the pointer is incremented by the number of bytes which were written.
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.Pp
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Objects that are not capable of seeking always write from the current
|
2004-07-02 23:52:20 +00:00
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position.
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The value of the pointer associated with such an object
|
1994-05-27 05:00:24 +00:00
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is undefined.
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.Pp
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|
If the real user is not the super-user, then
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.Fn write
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clears the set-user-id bit on a file.
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|
This prevents penetration of system security
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by a user who
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.Dq captures
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a writable set-user-id file
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owned by the super-user.
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.Pp
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|
When using non-blocking I/O on objects such as sockets that are subject
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to flow control,
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.Fn write
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and
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.Fn writev
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may write fewer bytes than requested;
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the return value must be noted,
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and the remainder of the operation should be retried when possible.
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.Sh RETURN VALUES
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Upon successful completion the number of bytes which were written
|
2004-07-02 23:52:20 +00:00
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is returned.
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Otherwise a -1 is returned and the global variable
|
1994-05-27 05:00:24 +00:00
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|
|
.Va errno
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is set to indicate the error.
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|
.Sh ERRORS
|
2002-12-18 09:22:32 +00:00
|
|
|
The
|
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.Fn write ,
|
1999-04-11 21:14:40 +00:00
|
|
|
.Fn writev ,
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.Fn pwrite
|
2005-07-07 18:17:55 +00:00
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|
and
|
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|
.Fn pwritev
|
2002-12-18 09:22:32 +00:00
|
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|
system calls
|
1994-05-27 05:00:24 +00:00
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|
will fail and the file pointer will remain unchanged if:
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.Bl -tag -width Er
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.It Bq Er EBADF
|
2002-12-19 09:40:28 +00:00
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|
The
|
2013-09-12 00:53:38 +00:00
|
|
|
.Fa fd
|
2002-12-19 09:40:28 +00:00
|
|
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argument
|
1994-05-27 05:00:24 +00:00
|
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|
is not a valid descriptor open for writing.
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.It Bq Er EPIPE
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|
An attempt is made to write to a pipe that is not open
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|
for reading by any process.
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|
.It Bq Er EPIPE
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|
An attempt is made to write to a socket of type
|
1996-09-28 13:32:35 +00:00
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|
.Dv SOCK_STREAM
|
1994-05-27 05:00:24 +00:00
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that is not connected to a peer socket.
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.It Bq Er EFBIG
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An attempt was made to write a file that exceeds the process's
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|
file size limit or the maximum file size.
|
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|
.It Bq Er EFAULT
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|
Part of
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.Fa iov
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|
or data to be written to the file
|
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|
points outside the process's allocated address space.
|
|
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|
.It Bq Er EINVAL
|
|
|
|
The pointer associated with
|
2013-09-12 00:53:38 +00:00
|
|
|
.Fa fd
|
1994-05-27 05:00:24 +00:00
|
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|
was negative.
|
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|
.It Bq Er ENOSPC
|
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|
There is no free space remaining on the file system
|
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|
containing the file.
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|
.It Bq Er EDQUOT
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|
|
The user's quota of disk blocks on the file system
|
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|
|
containing the file has been exhausted.
|
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|
.It Bq Er EIO
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|
|
|
An I/O error occurred while reading from or writing to the file system.
|
2001-02-26 09:38:01 +00:00
|
|
|
.It Bq Er EINTR
|
|
|
|
A signal interrupted the write before it could be completed.
|
1994-05-27 05:00:24 +00:00
|
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|
.It Bq Er EAGAIN
|
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|
The file was marked for non-blocking I/O,
|
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|
and no data could be written immediately.
|
2002-10-10 19:16:10 +00:00
|
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|
.It Bq Er EROFS
|
|
|
|
An attempt was made to write over a disk label area at the beginning
|
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|
of a slice.
|
|
|
|
Use
|
|
|
|
.Xr disklabel 8
|
|
|
|
.Fl W
|
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|
to enable writing on the disk label area.
|
2005-02-10 20:09:01 +00:00
|
|
|
.It Bq Er EINVAL
|
|
|
|
The value
|
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|
.Fa nbytes
|
|
|
|
is greater than
|
2017-10-17 02:51:45 +00:00
|
|
|
.Dv SSIZE_MAX
|
|
|
|
(or greater than
|
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|
|
.Dv INT_MAX ,
|
|
|
|
if the sysctl
|
|
|
|
.Va debug.iosize_max_clamp
|
|
|
|
is non-zero).
|
2020-03-30 21:44:00 +00:00
|
|
|
.It Bq Er EINTEGRITY
|
|
|
|
The backing store for
|
|
|
|
.Fa fd
|
|
|
|
detected corrupted data while reading.
|
|
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|
(For example, writing a partial filesystem block may require first reading
|
|
|
|
the existing block which may trigger this error.)
|
1994-05-27 05:00:24 +00:00
|
|
|
.El
|
|
|
|
.Pp
|
|
|
|
In addition,
|
|
|
|
.Fn writev
|
2005-07-07 18:17:55 +00:00
|
|
|
and
|
|
|
|
.Fn pwritev
|
1994-05-27 05:00:24 +00:00
|
|
|
may return one of the following errors:
|
|
|
|
.Bl -tag -width Er
|
1999-05-04 20:07:44 +00:00
|
|
|
.It Bq Er EDESTADDRREQ
|
|
|
|
The destination is no longer available when writing to a
|
|
|
|
.Ux
|
|
|
|
domain datagram socket on which
|
|
|
|
.Xr connect 2
|
|
|
|
had been used to set a destination address.
|
1994-05-27 05:00:24 +00:00
|
|
|
.It Bq Er EINVAL
|
2002-12-19 09:40:28 +00:00
|
|
|
The
|
|
|
|
.Fa iovcnt
|
|
|
|
argument
|
1994-05-27 05:00:24 +00:00
|
|
|
was less than or equal to 0, or greater than
|
2003-10-11 20:47:44 +00:00
|
|
|
.Dv IOV_MAX .
|
1994-05-27 05:00:24 +00:00
|
|
|
.It Bq Er EINVAL
|
|
|
|
One of the
|
|
|
|
.Fa iov_len
|
|
|
|
values in the
|
|
|
|
.Fa iov
|
|
|
|
array was negative.
|
|
|
|
.It Bq Er EINVAL
|
|
|
|
The sum of the
|
|
|
|
.Fa iov_len
|
2020-10-26 00:37:31 +00:00
|
|
|
values is greater than
|
|
|
|
.Dv SSIZE_MAX
|
|
|
|
(or greater than
|
|
|
|
.Dv INT_MAX ,
|
|
|
|
if the sysctl
|
|
|
|
.Va debug.iosize_max_clamp
|
|
|
|
is non-zero).
|
1999-07-30 21:20:09 +00:00
|
|
|
.It Bq Er ENOBUFS
|
|
|
|
The mbuf pool has been completely exhausted when writing to a socket.
|
1994-05-27 05:00:24 +00:00
|
|
|
.El
|
1999-04-11 21:14:40 +00:00
|
|
|
.Pp
|
|
|
|
The
|
|
|
|
.Fn pwrite
|
2005-07-07 18:17:55 +00:00
|
|
|
and
|
|
|
|
.Fn pwritev
|
|
|
|
system calls may also return the following errors:
|
1999-04-11 21:14:40 +00:00
|
|
|
.Bl -tag -width Er
|
|
|
|
.It Bq Er EINVAL
|
2004-10-25 13:35:03 +00:00
|
|
|
The
|
|
|
|
.Fa offset
|
|
|
|
value was negative.
|
1999-04-11 21:14:40 +00:00
|
|
|
.It Bq Er ESPIPE
|
|
|
|
The file descriptor is associated with a pipe, socket, or FIFO.
|
|
|
|
.El
|
1994-05-27 05:00:24 +00:00
|
|
|
.Sh SEE ALSO
|
|
|
|
.Xr fcntl 2 ,
|
|
|
|
.Xr lseek 2 ,
|
|
|
|
.Xr open 2 ,
|
|
|
|
.Xr pipe 2 ,
|
|
|
|
.Xr select 2
|
|
|
|
.Sh STANDARDS
|
1996-12-02 20:03:58 +00:00
|
|
|
The
|
|
|
|
.Fn write
|
2002-12-18 09:22:32 +00:00
|
|
|
system call is expected to conform to
|
1996-12-02 20:03:58 +00:00
|
|
|
.St -p1003.1-90 .
|
1999-04-11 21:14:40 +00:00
|
|
|
The
|
|
|
|
.Fn writev
|
|
|
|
and
|
|
|
|
.Fn pwrite
|
2002-12-18 09:22:32 +00:00
|
|
|
system calls are expected to conform to
|
1999-04-11 21:14:40 +00:00
|
|
|
.St -xpg4.2 .
|
1994-05-27 05:00:24 +00:00
|
|
|
.Sh HISTORY
|
|
|
|
The
|
2005-07-07 18:17:55 +00:00
|
|
|
.Fn pwritev
|
|
|
|
system call appeared in
|
|
|
|
.Fx 6.0 .
|
|
|
|
The
|
1999-04-11 21:14:40 +00:00
|
|
|
.Fn pwrite
|
2002-12-18 09:22:32 +00:00
|
|
|
function appeared in
|
1999-04-11 21:14:40 +00:00
|
|
|
.At V.4 .
|
|
|
|
The
|
1994-05-27 05:00:24 +00:00
|
|
|
.Fn writev
|
2002-12-18 09:22:32 +00:00
|
|
|
system call appeared in
|
1994-05-27 05:00:24 +00:00
|
|
|
.Bx 4.2 .
|
2002-12-18 09:22:32 +00:00
|
|
|
The
|
1996-08-22 23:31:07 +00:00
|
|
|
.Fn write
|
2002-12-18 09:22:32 +00:00
|
|
|
function appeared in
|
2017-12-01 22:26:36 +00:00
|
|
|
.At v1 .
|
2021-02-20 08:03:15 +00:00
|
|
|
.Sh BUGS
|
|
|
|
The
|
|
|
|
.Fn pwrite
|
|
|
|
system call appends the file without changing the file offset if
|
|
|
|
.Dv O_APPEND
|
|
|
|
is set, contrary to
|
|
|
|
.St -p1003.1-2008
|
|
|
|
where
|
|
|
|
.Fn pwrite
|
|
|
|
writes into
|
|
|
|
.Fa offset
|
|
|
|
regardless of whether
|
|
|
|
.Dv O_APPEND
|
|
|
|
is set.
|