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.\" Hey Emacs! This file is -*- nroff -*- source.
.\"
.\" Copyright (c) 1992 Drew Eckhardt (drew@cs.colorado.edu), March 28, 1992
.\"
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Permission is granted to copy and distribute modified versions of this
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one.
.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date. The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" the use of the information contained herein. The author(s) may not
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\"
.\" Modified by Michael Haardt <michael@moria.de>
.\" Modified Sat Jul 24 12:02:47 1993 by Rik Faith <faith@cs.unc.edu>
.\" Modified 15 Apr 1995 by Michael Chastain <mec@shell.portal.com>:
.\" Added reference to `bdflush(2)'.
.\" Modified 960414 by Andries Brouwer <aeb@cwi.nl>:
.\" Added the fact that since 1.3.20 sync actually waits.
.\" Modified Tue Oct 22 22:27:07 1996 by Eric S. Raymond <esr@thyrsus.com>
.\" Modified 2001-10-10 by aeb, following Michael Kerrisk.
.\"
.TH SYNC 2 2007-07-26 "Linux" "Linux Programmer's Manual"
.SH NAME
sync \- commit buffer cache to disk
.SH SYNOPSIS
.B #include <unistd.h>
.sp
.B void sync(void);
.sp
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.sp
.BR sync ():
.ad l
.RS 4
_BSD_SOURCE || _XOPEN_SOURCE >= 500 || _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
.RE
.ad
.SH DESCRIPTION
.BR sync ()
first commits inodes to buffers, and then buffers to disk.
.SH ERRORS
This function is always successful.
.SH "CONFORMING TO"
SVr4, 4.3BSD, POSIX.1-2001.
.SH NOTES
Since glibc 2.2.2 the Linux prototype is as listed above,
following the various standards.
In libc4, libc5, and glibc up to 2.2.1
it was "int sync(void)", and
.BR sync ()
always returned 0.
.SH BUGS
According to the standard specification (e.g., POSIX.1-2001),
.BR sync ()
schedules the writes, but may return before the actual
writing is done.
However, since version 1.3.20 Linux does actually wait.
(This still does not guarantee data integrity: modern disks have
large caches.)
.SH "SEE ALSO"
.BR bdflush (2),
.BR fdatasync (2),
.BR fsync (2),
.BR sync (8),
.BR update (8)
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