1.\" Copyright (c) 1980, 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. All advertising materials mentioning features or use of this software 13.\" must display the following acknowledgement: 14.\" This product includes software developed by the University of 15.\" California, Berkeley and its contributors. 16.\" 4. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" @(#)write.2 8.5 (Berkeley) 4/2/94 33.\" $FreeBSD: src/lib/libc/sys/write.2,v 1.12.2.8 2002/10/13 17:42:14 schweikh Exp $ 34.\" $DragonFly: src/lib/libc/sys/write.2,v 1.2 2003/06/17 04:26:47 dillon Exp $ 35.\" 36.Dd April 2, 1994 37.Dt WRITE 2 38.Os 39.Sh NAME 40.Nm write , 41.Nm writev , 42.Nm pwrite 43.Nd write output 44.Sh LIBRARY 45.Lb libc 46.Sh SYNOPSIS 47.In sys/types.h 48.In sys/uio.h 49.In unistd.h 50.Ft ssize_t 51.Fn write "int d" "const void *buf" "size_t nbytes" 52.Ft ssize_t 53.Fn writev "int d" "const struct iovec *iov" "int iovcnt" 54.Ft ssize_t 55.Fn pwrite "int d" "const void *buf" "size_t nbytes" "off_t offset" 56.Sh DESCRIPTION 57.Fn Write 58attempts to write 59.Fa nbytes 60of data to the object referenced by the descriptor 61.Fa d 62from the buffer pointed to by 63.Fa buf . 64.Fn Writev 65performs the same action, but gathers the output data 66from the 67.Fa iovcnt 68buffers specified by the members of the 69.Fa iov 70array: iov[0], iov[1], ..., iov[iovcnt\|-\|1]. 71.Fn Pwrite 72performs the same function, but writes to the specified position in 73the file without modifying the file pointer. 74.Pp 75For 76.Fn writev , 77the 78.Fa iovec 79structure is defined as: 80.Pp 81.Bd -literal -offset indent -compact 82struct iovec { 83 char *iov_base; /* Base address. */ 84 size_t iov_len; /* Length. */ 85}; 86.Ed 87.Pp 88Each 89.Fa iovec 90entry specifies the base address and length of an area 91in memory from which data should be written. 92.Fn Writev 93will always write a complete area before proceeding 94to the next. 95.Pp 96On objects capable of seeking, the 97.Fn write 98starts at a position 99given by the pointer associated with 100.Fa d , 101see 102.Xr lseek 2 . 103Upon return from 104.Fn write , 105the pointer is incremented by the number of bytes which were written. 106.Pp 107Objects that are not capable of seeking always write from the current 108position. The value of the pointer associated with such an object 109is undefined. 110.Pp 111If the real user is not the super-user, then 112.Fn write 113clears the set-user-id bit on a file. 114This prevents penetration of system security 115by a user who 116.Dq captures 117a writable set-user-id file 118owned by the super-user. 119.Pp 120When using non-blocking I/O on objects such as sockets that are subject 121to flow control, 122.Fn write 123and 124.Fn writev 125may write fewer bytes than requested; 126the return value must be noted, 127and the remainder of the operation should be retried when possible. 128.Sh RETURN VALUES 129Upon successful completion the number of bytes which were written 130is returned. Otherwise a -1 is returned and the global variable 131.Va errno 132is set to indicate the error. 133.Sh ERRORS 134.Fn Write , 135.Fn writev , 136and 137.Fn pwrite 138will fail and the file pointer will remain unchanged if: 139.Bl -tag -width Er 140.It Bq Er EBADF 141.Fa D 142is not a valid descriptor open for writing. 143.It Bq Er EPIPE 144An attempt is made to write to a pipe that is not open 145for reading by any process. 146.It Bq Er EPIPE 147An attempt is made to write to a socket of type 148.Dv SOCK_STREAM 149that is not connected to a peer socket. 150.It Bq Er EFBIG 151An attempt was made to write a file that exceeds the process's 152file size limit or the maximum file size. 153.It Bq Er EFAULT 154Part of 155.Fa iov 156or data to be written to the file 157points outside the process's allocated address space. 158.It Bq Er EINVAL 159The pointer associated with 160.Fa d 161was negative. 162.It Bq Er ENOSPC 163There is no free space remaining on the file system 164containing the file. 165.It Bq Er EDQUOT 166The user's quota of disk blocks on the file system 167containing the file has been exhausted. 168.It Bq Er EIO 169An I/O error occurred while reading from or writing to the file system. 170.It Bq Er EINTR 171A signal interrupted the write before it could be completed. 172.It Bq Er EAGAIN 173The file was marked for non-blocking I/O, 174and no data could be written immediately. 175.It Bq Er EROFS 176An attempt was made to write over a disk label area at the beginning 177of a disk. 178Use 179.Xr disklabel 8 180.Fl W 181to enable writing on the disk label area. 182.El 183.Pp 184In addition, 185.Fn writev 186may return one of the following errors: 187.Bl -tag -width Er 188.It Bq Er EDESTADDRREQ 189The destination is no longer available when writing to a 190.Ux 191domain datagram socket on which 192.Xr connect 2 193had been used to set a destination address. 194.It Bq Er EINVAL 195.Fa Iovcnt 196was less than or equal to 0, or greater than 197.Dv UIO_MAXIOV . 198.It Bq Er EINVAL 199One of the 200.Fa iov_len 201values in the 202.Fa iov 203array was negative. 204.It Bq Er EINVAL 205The sum of the 206.Fa iov_len 207values in the 208.Fa iov 209array overflowed a 32-bit integer. 210.It Bq Er ENOBUFS 211The mbuf pool has been completely exhausted when writing to a socket. 212.El 213.Pp 214The 215.Fn pwrite 216call may also return the following errors: 217.Bl -tag -width Er 218.It Bq Er EINVAL 219The specified file offset is invalid. 220.It Bq Er ESPIPE 221The file descriptor is associated with a pipe, socket, or FIFO. 222.El 223.Sh SEE ALSO 224.Xr fcntl 2 , 225.Xr lseek 2 , 226.Xr open 2 , 227.Xr pipe 2 , 228.Xr select 2 229.Sh STANDARDS 230The 231.Fn write 232function call is expected to conform to 233.St -p1003.1-90 . 234The 235.Fn writev 236and 237.Fn pwrite 238functions are expected to conform to 239.St -xpg4.2 . 240.Sh HISTORY 241The 242.Fn pwrite 243function call 244appeared in 245.At V.4 . 246The 247.Fn writev 248function call 249appeared in 250.Bx 4.2 . 251A 252.Fn write 253function call appeared in 254.At v6 . 255