.\" Copyright (c) 1992 Drew Eckhardt (drew@cs.colorado.edu), March 28, 1992

.\" and Copyright (c) 2011 Michael Kerrisk <mtk.manpages@gmail.com>

.\"

.\" %%%LICENSE_START(VERBATIM)

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.\" manual provided the copyright notice and this permission notice are

.\" preserved on all copies.

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.\" 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.

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.\" 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.\" manual page may be incorrect or out-of-date.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,

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.\"

.\" 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.

.\" 2011-09-07, mtk, Added syncfs() documentation,

.\"

.TH SYNC 2 2017-09-15 "Linux" "Linux Programmer's Manual"

.SH NAME

sync, syncfs \- commit filesystem caches to disk

.SH SYNOPSIS

.B #include <unistd.h>

.PP

.B void sync(void);

.PP

.BI "int syncfs(int " fd );

.PP

.in -4n

Feature Test Macro Requirements for glibc (see

.BR feature_test_macros (7)):

.in

.PP

.BR sync ():

.ad l

.RS 4

_XOPEN_SOURCE\ >=\ 500

.\"    || _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED

    || /* Since glibc 2.19: */ _DEFAULT_SOURCE

    || /* Glibc versions <= 2.19: */ _BSD_SOURCE

.RE

.ad

.PP

.BR syncfs ():

.ad l

.RS 4

_GNU_SOURCE

.RE

.ad

.SH DESCRIPTION

.BR sync ()

causes all pending modifications to filesystem metadata and cached file

data to be written to the underlying filesystems.

.PP

.BR syncfs ()

is like

.BR sync (),

but synchronizes just the filesystem containing file

referred to by the open file descriptor

.IR fd .

.SH RETURN VALUE

.BR syncfs ()

returns 0 on success;

on error, it returns \-1 and sets

.I errno

to indicate the error.

.SH ERRORS

.BR sync ()

is always successful.

.PP

.BR syncfs ()

can fail for at least the following reason:

.TP

.B EBADF

.I fd

is not a valid file descriptor.

.SH VERSIONS

.BR syncfs ()

first appeared in Linux 2.6.39;

library support was added to glibc in version 2.14.

.SH CONFORMING TO

.BR sync ():

POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.

.PP

.BR syncfs ()

is Linux-specific.

.SH NOTES

Since glibc 2.2.2, the Linux prototype for

.BR sync ()

is as listed above,

following the various standards.

In glibc 2.2.1 and earlier,

it was "int sync(void)", and

.BR sync ()

always returned 0.

.PP

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 Linux waits for I/O completions,

and thus

.BR sync ()

or

.BR syncfs ()

provide the same guarantees as fsync called on every file in

the system or filesystem respectively.

.SH BUGS

Before version 1.3.20 Linux did not wait for I/O to complete

before returning.

.SH SEE ALSO

.BR sync (1),

.BR fdatasync (2),

.BR fsync (2)

.SH COLOPHON

This page is part of release 4.15 of the Linux

.I man-pages

project.

A description of the project,

information about reporting bugs,

and the latest version of this page,

can be found at

\%https://www.kernel.org/doc/man\-pages/.