2fe8fb192f
There is important information about booting non-ack images in docs/UPDATING. ack/aout-format images can't be built any more, and booting clang/ELF-format ones is a little different. Updating to the new boot monitor is recommended. Changes in this commit: . drop boot monitor -> allowing dropping ack support . facility to copy ELF boot files to /boot so that old boot monitor can still boot fairly easily, see UPDATING . no more ack-format libraries -> single-case libraries . some cleanup of OBJECT_FMT, COMPILER_TYPE, etc cases . drop several ack toolchain commands, but not all support commands (e.g. aal is gone but acksize is not yet). . a few libc files moved to netbsd libc dir . new /bin/date as minix date used code in libc/ . test compile fix . harmonize includes . /usr/lib is no longer special: without ack, /usr/lib plays no kind of special bootstrapping role any more and bootstrapping is done exclusively through packages, so releases depend even less on the state of the machine making them now. . rename nbsd_lib* to lib* . reduce mtree
103 lines
3.3 KiB
Groff
103 lines
3.3 KiB
Groff
.\" $NetBSD: sync.2,v 1.17 2009/03/25 06:46:21 wiz Exp $
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.\"
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.\" Copyright (c) 1980, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)sync.2 8.1 (Berkeley) 6/4/93
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.\"
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.Dd March 25, 2009
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.Dt SYNC 2
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.Os
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.Sh NAME
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.Nm sync
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.Nd "synchronize disk block in-core status with that on disk"
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In unistd.h
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.Ft void
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.Fn sync void
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.Sh DESCRIPTION
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The
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.Fn sync
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function forces a write of dirty (modified) buffers
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in the block buffer cache out
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to disk.
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The kernel keeps this information in core to reduce
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the number of disk I/O transfers required by the system.
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As information in the cache is lost after a system crash,
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kernel thread
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.Nm ioflush
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ensures that dirty buffers are synced to disk
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eventually.
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By default, a dirty buffer is synced after 30 seconds,
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but some filesystems exploit
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.Nm ioflush
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features to sync directory data and metadata faster
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(after 15 and 10 seconds, respectively).
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.Pp
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The function
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.Xr fsync 2
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may be used to synchronize individual file descriptor
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attributes.
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.Sh CAUTIONS
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Many modern disks contain write-back caches.
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In theory
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.Fn sync
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flushes these.
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In practice there are many possible ways for this mechanism to go
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astray.
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It is prudent (where possible) to allow a few seconds after syncing
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for everything to settle before e.g. turning off the power.
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.Pp
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It may also be desirable to use
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.Xr dkctl 8
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or
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.Xr scsictl 8
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to disable the write-back cache entirely.
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.Sh SEE ALSO
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.Xr fsync 2 ,
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.Xr dkctl 8 ,
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.Xr scsictl 8 ,
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.Xr sync 8
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.Sh HISTORY
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A
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.Fn sync
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function call appeared in
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.At v6 .
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.Pp
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Historically,
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.Fn sync
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would schedule buffers for writing but not actually wait for the
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writes to finish.
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It was necessary to issue a second or sometimes a third call to ensure
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that all buffers had in fact been written out.
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In
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.Nx ,
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.Fn sync
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does not return until all buffers have been written.
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