sync - synchronize data on disk with memory
SYNOPSYS
sync [--help] [--version]
DESCRIPTION
sync 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; The sync program does noth
ing but exercise the sync(2) system call.
The kernel keeps data in memory to avoid doing (relatively
slow) disk reads and writes. This improves performance,
but if the computer crashes, data may be lost or the
filesystem corrupted as a result. sync ensures everything
in memory is written to disk.
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 shutdown(8) or reboot(8) or
halt(8) commands, which will attempt to put the system in
a quiescent state before calling sync(2). (Various imple
mentations of these commands exist; consult your documen
tation; on some systems one should not call reboot(8) and
halt(8) directly.)
GNU STANDARD OPTIONS
--help Print a usage message on standard output and exit
successfully.
--version
Print version information on standard output, then
exit successfully.
-- Terminate option list.
ENVIRONMENT
The variables LANG, LC_ALL, LC_CTYPE and LC_MESSAGES have
the usual meaning.
CONFORMING TO
POSIX 1003.2
NOTES
On Linux, 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 reboot(8)
and halt(8) commands take this into account by sleeping
for a few seconds after calling sync(2).
This page describes sync as found in the fileutils-4.0
tions and additions to aeb@cwi.nl. Report bugs in the
program to fileutils-bugs@gnu.ai.mit.edu.
SEE ALSO
sync(2), halt(8), reboot(8), update(8)
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