2004-11-03 13:51:07 +00:00
|
|
|
.\" Reboot/halt and Linux information extracted from Rick Faith's original
|
|
|
|
.\" sync(8) manpage, dating back to the Linux 0.99 days. The Linux-specific
|
|
|
|
.\" information is attributed to Linus Torvalds
|
|
|
|
.\" Copyright 1992, 1993 Rickard E. Faith (faith@cs.unc.edu)
|
|
|
|
.\" May be distributed under the GNU General Public License
|
2007-05-18 10:09:18 +00:00
|
|
|
.TH SYNC 8 1998-11-01 "GNU" "Linux Programmer's Manual"
|
2004-11-03 13:51:07 +00:00
|
|
|
.SH NAME
|
|
|
|
sync \- synchronize data on disk with memory
|
2005-06-24 14:17:21 +00:00
|
|
|
.SH SYNOPSIS
|
2004-11-03 13:51:07 +00:00
|
|
|
.B "sync [\-\-help] [\-\-version]"
|
|
|
|
.SH DESCRIPTION
|
|
|
|
.B sync
|
2007-04-12 22:42:49 +00:00
|
|
|
writes any data buffered in memory out to disk.
|
|
|
|
This can include (but is not limited to) modified superblocks,
|
|
|
|
modified inodes, and delayed reads and writes.
|
|
|
|
This must be implemented by the kernel;
|
2004-11-03 13:51:07 +00:00
|
|
|
The
|
|
|
|
.B sync
|
|
|
|
program does nothing but exercise the
|
|
|
|
.BR sync (2)
|
|
|
|
system call.
|
|
|
|
.PP
|
|
|
|
The kernel keeps data in memory to avoid doing (relatively slow) disk
|
2007-04-12 22:42:49 +00:00
|
|
|
reads and writes.
|
|
|
|
This improves performance, but if the computer
|
2004-11-03 13:51:07 +00:00
|
|
|
crashes, data may be lost or the filesystem corrupted as a result.
|
|
|
|
.B sync
|
|
|
|
ensures that everything in memory is written to disk.
|
|
|
|
.PP
|
|
|
|
.B sync
|
|
|
|
should be called before the processor is halted in an unusual manner
|
|
|
|
(e.g., before causing a kernel panic when debugging new kernel code).
|
|
|
|
In general, the processor should be halted using the
|
|
|
|
.BR shutdown (8)
|
|
|
|
or
|
|
|
|
.BR reboot (8)
|
|
|
|
or
|
|
|
|
.BR halt (8)
|
|
|
|
commands, which will attempt to put the system in a quiescent state
|
|
|
|
before calling
|
|
|
|
.BR sync (2).
|
|
|
|
(Various implementations of these commands exist; consult your
|
|
|
|
documentation; on some systems one should not call
|
|
|
|
.BR reboot (8)
|
|
|
|
and
|
|
|
|
.BR halt (8)
|
|
|
|
directly.)
|
2007-05-16 05:06:47 +00:00
|
|
|
.SH "OPTIONS"
|
2004-11-03 13:51:07 +00:00
|
|
|
.TP
|
|
|
|
.B "\-\-help"
|
|
|
|
Print a usage message on standard output and exit successfully.
|
|
|
|
.TP
|
|
|
|
.B "\-\-version"
|
|
|
|
Print version information on standard output, then exit successfully.
|
|
|
|
.TP
|
|
|
|
.B "\-\-"
|
|
|
|
Terminate option list.
|
|
|
|
.SH ENVIRONMENT
|
|
|
|
The variables LANG, LC_ALL, LC_CTYPE, and LC_MESSAGES have the
|
|
|
|
usual meaning.
|
|
|
|
.SH "CONFORMING TO"
|
2006-08-03 13:58:36 +00:00
|
|
|
POSIX.2
|
2004-11-03 13:51:07 +00:00
|
|
|
.SH NOTES
|
|
|
|
On Linux,
|
|
|
|
.B sync
|
|
|
|
is only guaranteed to schedule the dirty blocks for writing; it can
|
|
|
|
actually take a short time before all the blocks are finally written.
|
|
|
|
The
|
|
|
|
.BR reboot (8)
|
|
|
|
and
|
|
|
|
.BR halt (8)
|
|
|
|
commands take this into account by sleeping for a few seconds after
|
|
|
|
calling
|
|
|
|
.BR sync (2).
|
|
|
|
.PP
|
|
|
|
This page describes
|
|
|
|
.B sync
|
|
|
|
as found in the file\%utils-4.0 package;
|
|
|
|
other versions may differ slightly.
|
|
|
|
.SH "SEE ALSO"
|
|
|
|
.BR sync (2),
|
|
|
|
.BR halt (8),
|
|
|
|
.BR reboot (8),
|
|
|
|
.BR update (8)
|