SYNC(8) Linux Programmer's Manual SYNC(8) NAME sync - synchronize data on disk with memory SYNOPSIS 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 nothing 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 file system corrupted as a result. sync ensures that everything in memory is written to disk. sync should be called before the processor is halted in an unusual man- ner (e.g., before causing a kernel panic when debugging new kernel code). In general, the processor should be halted using the shut- down(8) or reboot(8) or halt(8) commands, which will attempt to put the system in a quiescent state before calling sync(2). (Various implemen- tations of these commands exist; consult your documentation; on some systems one should not call reboot(8) and halt(8) directly.) OPTIONS --help Print a usage message on standard output and exit successfully. --version Print version information on standard output, then exit success- fully. -- Terminate option list. ENVIRONMENT The variables LANG, LC_ALL, LC_CTYPE, and LC_MESSAGES have the usual meaning. CONFORMING TO POSIX.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 package; other versions may differ slightly. SEE ALSO sync(2), halt(8), reboot(8), update(8) COLOPHON This page is part of release 3.27 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/. GNU 1998-11-01 SYNC(8)
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