139 lines
5.4 KiB
Perl
139 lines
5.4 KiB
Perl
.\" $NetBSD: b.t,v 1.1 2007/12/18 03:35:54 garbled Exp $
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.\" Copyright (c) 1983, 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. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. 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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.\" @(#)b.t 8.1 (Berkeley) 6/8/93
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.\"
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.\".ds RH "Device Defaulting Rules
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.bp
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.LG
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.B
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.ce
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APPENDIX B. RULES FOR DEFAULTING SYSTEM DEVICES
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.sp
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.R
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.NL
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.PP
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When \fIconfig\fP processes a ``config'' rule which does
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not fully specify the location of the root file system,
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paging area(s), device for system dumps, and device for
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argument list processing it applies a set of rules to
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define those values left unspecified. The following list
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of rules are used in defaulting system devices.
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.IP 1) 3
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If a root device is not specified, the swap
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specification must indicate a ``generic'' system is to be built.
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.IP 2) 3
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If the root device does not specify a unit number, it
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defaults to unit 0.
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.IP 3) 3
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If the root device does not include a partition specification,
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it defaults to the ``a'' partition.
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.IP 4) 3
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If no swap area is specified, it defaults to the ``b''
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partition of the root device.
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.IP 5) 3
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If no device is specified for processing argument lists, the
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first swap partition is selected.
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.IP 6) 3
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If no device is chosen for system dumps, the first swap
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partition is selected (see below to find out where dumps are
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placed within the partition).
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.PP
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The following table summarizes the default partitions selected
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when a device specification is incomplete, e.g. ``hp0''.
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.DS
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.TS
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l l.
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Type Partition
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_
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root ``a''
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swap ``b''
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args ``b''
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dumps ``b''
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.TE
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.DE
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.SH
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Multiple swap/paging areas
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.PP
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When multiple swap partitions are specified, the system treats the
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first specified as a ``primary'' swap area which is always used.
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The remaining partitions are then interleaved into the paging
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system at the time a
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.IR swapon (2)
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system call is made. This is normally done at boot time with
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a call to
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.IR swapon (8)
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from the /etc/rc file.
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.SH
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System dumps
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.PP
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System dumps are automatically taken after a system crash,
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provided the device driver for the ``dumps'' device supports
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this. The dump contains the contents of memory, but not
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the swap areas. Normally the dump device is a disk in
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which case the information is copied to a location at the
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back of the partition. The dump is placed in the back of the
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partition because the primary swap and dump device are commonly
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the same device and this allows the system to be rebooted without
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immediately overwriting the saved information. When a dump has
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occurred, the system variable \fIdumpsize\fP
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is set to a non-zero value indicating the size (in bytes) of
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the dump. The \fIsavecore\fP\|(8)
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program then copies the information from the dump partition to
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a file in a ``crash'' directory and also makes a copy of the
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system which was running at the time of the crash (usually
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``/kernel''). The offset to the system dump is defined in the
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system variable \fIdumplo\fP (a sector offset from
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the front of the dump partition). The
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.I savecore
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program operates by reading the contents of \fIdumplo\fP, \fIdumpdev\fP,
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and \fIdumpmagic\fP from /dev/kmem, then comparing the value
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of \fIdumpmagic\fP read from /dev/kmem to that located in
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corresponding location in the dump area of the dump partition.
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If a match is found,
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.I savecore
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assumes a crash occurred and reads \fIdumpsize\fP from the dump area
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of the dump partition. This value is then used in copying the
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system dump. Refer to
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\fIsavecore\fP\|(8)
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for more information about its operation.
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.PP
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The value \fIdumplo\fP is calculated to be
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.DS
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\fIdumpdev-size\fP \- \fImemsize\fP
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.DE
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where \fIdumpdev-size\fP is the size of the disk partition
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where system dumps are to be placed, and
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\fImemsize\fP is the size of physical memory.
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If the disk partition is not large enough to hold a full
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dump, \fIdumplo\fP is set to 0 (the start of the partition).
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