1.\" Copyright (c) 1983, 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.\" @(#)fsync.2 8.1 (Berkeley) 6/4/93 33.\" $FreeBSD$ 34.\" 35.Dd June 4, 1993 36.Dt FSYNC 2 37.Os 38.Sh NAME 39.Nm fsync 40.Nd "synchronise changes to a file" 41.Sh LIBRARY 42.Lb libc 43.Sh SYNOPSIS 44.Fd #include <unistd.h> 45.Ft int 46.Fn fsync "int fd" 47.Sh DESCRIPTION 48.Fn Fsync 49causes all modified data and attributes of 50.Fa fd 51to be moved to a permanent storage device. 52This normally results in all in-core modified copies 53of buffers for the associated file to be written to a disk. 54.Pp 55.Fn Fsync 56should be used by programs that require a file to be 57in a known state, for example, in building a simple transaction 58facility. 59.Sh IMPLEMENTATION NOTES 60In the non-threaded library 61.Fn fsync 62is implemented as the 63.Va fsync 64syscall. 65.Pp 66In the threaded library, the 67.Va fsync 68syscall is assembled to 69.Fn _thread_sys_fsync 70and 71.Fn fsync 72is implemented as a function which locks 73.Fa fd 74for read and write, then calls 75.Fn _thread_sys_fsync . 76Before returning, 77.Fn fsync 78unlocks 79.Fa fd . 80.Sh RETURN VALUES 81A 0 value is returned on success. A -1 value indicates 82an error. 83.Sh ERRORS 84The 85.Fn fsync 86fails if: 87.Bl -tag -width Er 88.It Bq Er EBADF 89.Fa fd 90is not a valid descriptor. 91.It Bq Er EINVAL 92.Fa fd 93refers to a socket, not to a file. 94.It Bq Er EIO 95An I/O error occurred while reading from or writing to the file system. 96.El 97.Sh SEE ALSO 98.Xr sync 2 , 99.Xr syncer 4 , 100.Xr sync 8 101.Sh HISTORY 102The 103.Fn fsync 104function call appeared in 105.Bx 4.2 . 106