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