-.\" Hey Emacs! This file is -*- nroff -*- source.
-.\"
.\" 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)
.\" 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.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
+.\" %%%LICENSE_END
.\"
.\" Modified by Michael Haardt <michael@moria.de>
.\" Modified Sat Jul 24 12:02:47 1993 by Rik Faith <faith@cs.unc.edu>
.\" 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 2010-09-20 "Linux" "Linux Programmer's Manual"
+.TH SYNC 2 2017-09-15 "Linux" "Linux Programmer's Manual"
.SH NAME
-sync \- commit buffer cache to disk
+sync, syncfs \- commit filesystem caches to disk
.SH SYNOPSIS
.B #include <unistd.h>
-.sp
+.PP
.B void sync(void);
-.sp
+.PP
+.BI "int syncfs(int " fd );
+.PP
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
-.sp
+.PP
.BR sync ():
.ad l
.RS 4
-_BSD_SOURCE || _XOPEN_SOURCE\ >=\ 500 ||
-_XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
+_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 buffered modifications to file metadata and data to be
-written to the underlying file systems.
+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.
-.SH "CONFORMING TO"
+.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 ():
-SVr4, 4.3BSD, POSIX.1-2001.
+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
+Since glibc 2.2.2, the Linux prototype for
.BR sync ()
is as listed above,
following the various standards.
-In libc4, libc5, and glibc up to 2.2.1
+In glibc 2.2.1 and earlier,
it was "int sync(void)", and
.BR sync ()
always returned 0.
-.SH BUGS
+.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, 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),
+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),
-.BR sync (8),
-.BR update (8)
+.BR fsync (2)
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