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Annotation of 43BSDReno/share/doc/smm/02.config/b.t, revision 1.1

1.1     ! root        1: .\" Copyright (c) 1983 Regents of the University of California.
        !             2: .\" All rights reserved.  The Berkeley software License Agreement
        !             3: .\" specifies the terms and conditions for redistribution.
        !             4: .\"
        !             5: .\"    @(#)b.t 6.2 (Berkeley) 6/3/86
        !             6: .\"
        !             7: .\".ds RH "Device Defaulting Rules
        !             8: .bp
        !             9: .LG
        !            10: .B
        !            11: .ce
        !            12: APPENDIX B. RULES FOR DEFAULTING SYSTEM DEVICES
        !            13: .sp
        !            14: .R
        !            15: .NL
        !            16: .PP
        !            17: When \fIconfig\fP processes a ``config'' rule which does
        !            18: not fully specify the location of the root file system,
        !            19: paging area(s), device for system dumps, and device for
        !            20: argument list processing it applies a set of rules to
        !            21: define those values left unspecified.  The following list
        !            22: of rules are used in defaulting system devices.
        !            23: .IP 1) 3
        !            24: If a root device is not specified, the swap
        !            25: specification must indicate a ``generic'' system is to be built.
        !            26: .IP 2) 3
        !            27: If the root device does not specify a unit number, it
        !            28: defaults to unit 0.
        !            29: .IP 3) 3
        !            30: If the root device does not include a partition specification,
        !            31: it defaults to the ``a'' partition.
        !            32: .IP 4) 3
        !            33: If no swap area is specified, it defaults to the ``b''
        !            34: partition of the root device.
        !            35: .IP 5) 3
        !            36: If no device is specified for processing argument lists, the
        !            37: first swap partition is selected.
        !            38: .IP 6) 3
        !            39: If no device is chosen for system dumps, the first swap
        !            40: partition is selected (see below to find out where dumps are
        !            41: placed within the partition).
        !            42: .PP
        !            43: The following table summarizes the default partitions selected
        !            44: when a device specification is incomplete, e.g. ``hp0''.
        !            45: .DS
        !            46: .TS
        !            47: l l.
        !            48: Type   Partition
        !            49: _
        !            50: root   ``a''
        !            51: swap   ``b''
        !            52: args   ``b''
        !            53: dumps  ``b''
        !            54: .TE
        !            55: .DE
        !            56: .SH
        !            57: Multiple swap/paging areas
        !            58: .PP
        !            59: When multiple swap partitions are specified, the system treats the
        !            60: first specified as a ``primary'' swap area which is always used.
        !            61: The remaining partitions are then interleaved into the paging
        !            62: system at the time a
        !            63: .IR swapon (2)
        !            64: system call is made.  This is normally done at boot time with
        !            65: a call to
        !            66: .IR swapon (8)
        !            67: from the /etc/rc file.
        !            68: .SH
        !            69: System dumps
        !            70: .PP
        !            71: System dumps are automatically taken after a system crash,
        !            72: provided the device driver for the ``dumps'' device supports
        !            73: this.  The dump contains the contents of memory, but not
        !            74: the swap areas.  Normally the dump device is a disk in
        !            75: which case the information is copied to a location at the
        !            76: back of the partition.  The dump is placed in the back of the
        !            77: partition because the primary swap and dump device are commonly
        !            78: the same device and this allows the system to be rebooted without
        !            79: immediately overwriting the saved information.  When a dump has
        !            80: occurred, the system variable \fIdumpsize\fP 
        !            81: is set to a non-zero value indicating the size (in bytes) of
        !            82: the dump.  The \fIsavecore\fP\|(8)
        !            83: program then copies the information from the dump partition to
        !            84: a file in a ``crash'' directory and also makes a copy of the
        !            85: system which was running at the time of the crash (usually
        !            86: ``/vmunix'').  The offset to the system dump is defined in the
        !            87: system variable \fIdumplo\fP (a sector offset from
        !            88: the front of the dump partition). The 
        !            89: .I savecore
        !            90: program operates by reading the contents of \fIdumplo\fP, \fIdumpdev\fP,
        !            91: and \fIdumpmagic\fP from /dev/kmem, then comparing the value
        !            92: of \fIdumpmagic\fP read from /dev/kmem to that located in
        !            93: corresponding location in the dump area of the dump partition.
        !            94: If a match is found, 
        !            95: .I savecore
        !            96: assumes a crash occurred and reads \fIdumpsize\fP from the dump area
        !            97: of the dump partition.  This value is then used in copying the
        !            98: system dump.  Refer to 
        !            99: \fIsavecore\fP\|(8)
        !           100: for more information about its operation.
        !           101: .PP
        !           102: The value \fIdumplo\fP is calculated to be 
        !           103: .DS
        !           104: \fIdumpdev-size\fP \- \fImemsize\fP
        !           105: .DE
        !           106: where \fIdumpdev-size\fP is the size of the disk partition
        !           107: where system dumps are to be placed, and
        !           108: \fImemsize\fP is the size of physical memory.
        !           109: If the disk partition is not large enough to hold a full
        !           110: dump, \fIdumplo\fP is set to 0 (the start of the partition).

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