1.\" Copyright (c) 1983, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" Copyright (c) 2016 The FreeBSD Foundation, Inc. 4.\" All rights reserved. 5.\" 6.\" Parts of this documentation were written by 7.\" Konstantin Belousov <[email protected]> under sponsorship 8.\" from the FreeBSD Foundation. 9.\" 10.\" Redistribution and use in source and binary forms, with or without 11.\" modification, are permitted provided that the following conditions 12.\" are met: 13.\" 1. Redistributions of source code must retain the above copyright 14.\" notice, this list of conditions and the following disclaimer. 15.\" 2. Redistributions in binary form must reproduce the above copyright 16.\" notice, this list of conditions and the following disclaimer in the 17.\" documentation and/or other materials provided with the distribution. 18.\" 3. 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.\" @(#)fsync.2 8.1 (Berkeley) 6/4/93 35.\" $FreeBSD$ 36.\" 37.Dd February 6, 2018 38.Dt FSYNC 2 39.Os 40.Sh NAME 41.Nm fdatasync , 42.Nm fsync 43.Nd "synchronise changes to a file" 44.Sh LIBRARY 45.Lb libc 46.Sh SYNOPSIS 47.In unistd.h 48.Ft int 49.Fn fdatasync "int fd" 50.Ft int 51.Fn fsync "int fd" 52.Sh DESCRIPTION 53The 54.Fn fsync 55system call 56causes all modified data and attributes of the file referenced by 57the file descriptor 58.Fa fd 59to be moved to a permanent storage device. 60This normally results in all in-core modified copies 61of buffers for the associated file to be written to a disk. 62.Pp 63The 64.Fn fdatasync 65system call causes all modified data of 66.Fa fd 67to be moved to a permanent storage device. 68Unlike 69.Fn fsync , 70the system call does not guarantee that file attributes or 71metadata necessary to access the file are committed to the permanent storage. 72.Pp 73The 74.Fn fsync 75system call 76should be used by programs that require a file to be 77in a known state, for example, in building a simple transaction 78facility. 79If the file metadata has already been committed, using 80.Fn fdatasync 81can be more efficient than 82.Fn fsync . 83.Pp 84Both 85.Fn fdatasync 86and 87.Fn fsync 88calls are cancellation points. 89.Sh RETURN VALUES 90.Rv -std fsync 91.Sh ERRORS 92The 93.Fn fsync 94and 95.Fn fdatasync 96calls fail if: 97.Bl -tag -width Er 98.It Bq Er EBADF 99The 100.Fa fd 101argument 102is not a valid descriptor. 103.It Bq Er EINVAL 104The 105.Fa fd 106argument 107refers to a socket, not to a file. 108.It Bq Er EIO 109An I/O error occurred while reading from or writing to the file system. 110.El 111.Sh SEE ALSO 112.Xr fsync 1 , 113.Xr sync 2 , 114.Xr syncer 4 , 115.Xr sync 8 116.Sh HISTORY 117The 118.Fn fsync 119system call appeared in 120.Bx 4.2 . 121The 122.Fn fdatasync 123system call appeared in 124.Fx 11.1 . 125.Sh BUGS 126The 127.Fn fdatasync 128system call currently does not guarantee that enqueued 129.Xr aio 4 130requests for the file referenced by 131.Fa fd 132are completed before the syscall returns. 133