man2/sync.2

   1 .\" Copyright (c) 1992 Drew Eckhardt (drew@cs.colorado.edu), March 28, 1992
   2 .\" and Copyright (c) 2011 Michael Kerrisk <mtk.manpages@gmail.com>
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  26 .\" Modified by Michael Haardt <michael@moria.de>
  27 .\" Modified Sat Jul 24 12:02:47 1993 by Rik Faith <faith@cs.unc.edu>
  28 .\" Modified 15 Apr 1995 by Michael Chastain <mec@shell.portal.com>:
  29 .\"   Added reference to `bdflush(2)'.
  30 .\" Modified 960414 by Andries Brouwer <aeb@cwi.nl>:
  31 .\"   Added the fact that since 1.3.20 sync actually waits.
  32 .\" Modified Tue Oct 22 22:27:07 1996 by Eric S. Raymond <esr@thyrsus.com>
  33 .\" Modified 2001-10-10 by aeb, following Michael Kerrisk.
  34 .\" 2011-09-07, mtk, Added syncfs() documentation,
  35 .\"
  36 .TH SYNC 2 2017-09-15 "Linux" "Linux Programmer's Manual"
  37 .SH NAME
  38 sync, syncfs \- commit filesystem caches to disk
  39 .SH SYNOPSIS
  40 .B #include <unistd.h>
  41 .PP
  42 .B void sync(void);
  43 .PP
  44 .BI "int syncfs(int " fd );
  45 .PP
  46 .in -4n
  47 Feature Test Macro Requirements for glibc (see
  48 .BR feature_test_macros (7)):
  49 .in
  50 .PP
  51 .BR sync ():
  52 .ad l
  53 .RS 4
  54 _XOPEN_SOURCE\ >=\ 500
  55 .\"    || _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
  56     || /* Since glibc 2.19: */ _DEFAULT_SOURCE
  57     || /* Glibc versions <= 2.19: */ _BSD_SOURCE
  58 .RE
  59 .ad
  60 .PP
  61 .BR syncfs ():
  62 .ad l
  63 .RS 4
  64 _GNU_SOURCE
  65 .RE
  66 .ad
  67 .SH DESCRIPTION
  68 .BR sync ()
  69 causes all pending modifications to filesystem metadata and cached file
  70 data to be written to the underlying filesystems.
  71 .PP
  72 .BR syncfs ()
  73 is like
  74 .BR sync (),
  75 but synchronizes just the filesystem containing file
  76 referred to by the open file descriptor
  77 .IR fd .
  78 .SH RETURN VALUE
  79 .BR syncfs ()
  80 returns 0 on success;
  81 on error, it returns \-1 and sets
  82 .I errno
  83 to indicate the error.
  84 .SH ERRORS
  85 .BR sync ()
  86 is always successful.
  87 .PP
  88 .BR syncfs ()
  89 can fail for at least the following reason:
  90 .TP
  91 .B EBADF
  92 .I fd
  93 is not a valid file descriptor.
  94 .SH VERSIONS
  95 .BR syncfs ()
  96 first appeared in Linux 2.6.39;
  97 library support was added to glibc in version 2.14.
  98 .SH CONFORMING TO
  99 .BR sync ():
 100 POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.
 101 .PP
 102 .BR syncfs ()
 103 is Linux-specific.
 104 .SH NOTES
 105 Since glibc 2.2.2, the Linux prototype for
 106 .BR sync ()
 107 is as listed above,
 108 following the various standards.
 109 In glibc 2.2.1 and earlier,
 110 it was "int sync(void)", and
 111 .BR sync ()
 112 always returned 0.
 113 .PP
 114 According to the standard specification (e.g., POSIX.1-2001),
 115 .BR sync ()
 116 schedules the writes, but may return before the actual
 117 writing is done.  However Linux waits for I/O completions,
 118 and thus
 119 .BR sync ()
 120 or
 121 .BR syncfs ()
 122 provide the same guarantees as fsync called on every file in
 123 the system or filesystem respectively.
 124 .SH BUGS
 125 Before version 1.3.20 Linux did not wait for I/O to complete
 126 before returning.
 127 .SH SEE ALSO
 128 .BR sync (1),
 129 .BR fdatasync (2),
 130 .BR fsync (2)