1SYNC(8) Linux Programmer's Manual SYNC(8)
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6 sync - synchronize data on disk with memory
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9 sync [--help] [--version]
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12 sync writes any data buffered in memory out to disk. This can include
13 (but is not limited to) modified superblocks, modified inodes, and
14 delayed reads and writes. This must be implemented by the kernel; The
15 sync program does nothing but exercise the sync(2) system call.
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17 The kernel keeps data in memory to avoid doing (relatively slow) disk
18 reads and writes. This improves performance, but if the computer
19 crashes, data may be lost or the file system corrupted as a result.
20 sync ensures that everything in memory is written to disk.
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22 sync should be called before the processor is halted in an unusual man‐
23 ner (e.g., before causing a kernel panic when debugging new kernel
24 code). In general, the processor should be halted using the shut‐
25 down(8) or reboot(8) or halt(8) commands, which will attempt to put the
26 system in a quiescent state before calling sync(2). (Various implemen‐
27 tations of these commands exist; consult your documentation; on some
28 systems one should not call reboot(8) and halt(8) directly.)
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31 --help Print a usage message on standard output and exit successfully.
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33 --version
34 Print version information on standard output, then exit success‐
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37 -- Terminate option list.
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40 The variables LANG, LC_ALL, LC_CTYPE, and LC_MESSAGES have the usual
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44 POSIX.2.
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47 On Linux, sync is only guaranteed to schedule the dirty blocks for
48 writing; it can actually take a short time before all the blocks are
49 finally written. The reboot(8) and halt(8) commands take this into
50 account by sleeping for a few seconds after calling sync(2).
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52 This page describes sync as found in the fileutils-4.0 package; other
53 versions may differ slightly.
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56 sync(2), halt(8), reboot(8), update(8)
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59 This page is part of release 3.25 of the Linux man-pages project. A
60 description of the project, and information about reporting bugs, can
61 be found at http://www.kernel.org/doc/man-pages/.
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65GNU 1998-11-01 SYNC(8)