installb.8

操作系统设计与实现源码

.TH INSTALLBOOT 8
.SH NAME
installboot \- make a device bootable
.SH SYNOPSIS
.B installboot \-i(mage)
.I image
.RI [ label :] kernel
.IR "mm fs" " ... " init
.br
.B installboot \-(e)x(tract)
.I image
.br
.B installboot \-d(evice)
.I device bootblock boot
.RI [[ label :] image
\&...]
.br
.B installboot \-b(oot)
.I device bootblock boot
.RI [ label :] image
\&...
.br
.B installboot \-m(aster)
.RI [ fix ]
.I device masterboot
.SH DESCRIPTION
.de SP
.if t .sp 0.4
.if n .sp
..
.B Installboot
may be used to make a device bootable by constructing a kernel image and
installing bootstrap code into the boot block of a Minix file system.  To
understand how this can be done one first has to know what happens when a
PC is booted.
.PP
When the power is turned on the typical PC will try to read the first sector
from the first floppy disk or from the first hard disk into memory and execute
it.  The code obtained from the hard disk (from the so-called master boot
sector) will immediately replace itself by the code found in the first sector
of the active partition.  Thus the PC is now executing the bootstrap code found
in the first sector of /dev/fd0, /dev/hd1, /dev/hd2, /dev/hd3, or /dev/hd4.
The bootstrap will locate the operating system on the device it itself was
loaded from, load it, and execute it.
.PP
To make a Minix file system
.B /dev/fd0
mounted on
.B /mnt
bootable, enter the following:
.SP
.RS
.ft B
cp /usr/mdec/boot /mnt/boot
.SP
installboot \-i /mnt/minix kernel mm fs init
.SP
installboot \-d /dev/fd0 /usr/mdec/bootblock boot
.ft P
.RE
.PP
The "boot" program in the example is named the "boot monitor".  It is loaded
by the bootblock code placed in the boot sector of /dev/fd0 and it will take
care of loading the kernel image "minix" from the root directory of the
file system.  See
.BR monitor (8)
for a description of the boot monitor.  Note that
.B boot
is a name in the file system on
.B /dev/fd0
in this example, the same file as
.BR /mnt/boot .
Making
.B /mnt/minix
is normally not necessary, there is usually a kernel image in the
.B tools
directory.
.SH OPTIONS
.B \-i(mage)
.I image
.RI [ label :] kernel
.IR "mm fs" " ... " init
.RS
The
.B \-image
option (or the
.B \-i
shorthand) combines the executable files needed to run Minix in one file.
Only the names and a few zero bytes are inserted into the image.  The name
is for identification and the zeros are used to pad separate pieces to
sector boundaries for fast loading.
.SP
An executable may be prefixed by a label.  The monitor may be instructed to
load processes by label.  So more than one kernel process may be included in
the image, each with a different winchester driver for instance.  So if you
have compiled two different kernels with an AT or XT driver then
.SP
.RS
.BI "installboot \-i" " image AT:at_kernel XT:xt_kernel mm fs init"
.RE
.SP
will make an image with two different labeled kernels and one
unlabeled set of the other binaries.
.RE
.PP
.B \-(e)x(tract)
.I image
.RS
Extract the binaries from
.I image
under the names stored in the image.  (The name includes the optional label.)
.RE
.PP
.B \-d(evice)
.I device bootblock boot
.RI [[ label :] image
\&...]
.RS
Installs
.I bootblock
in the boot sector of
.I device
together with the disk addresses to
.IR boot .
These disk addresses are needed to load
.I boot
from the file system at boot time.  The argument
.I boot
is first searched in the file system on
.IR device .
If it is not found then it is read as a normal file and added at the end of
the file system.  The file system should be smaller than the device it is on
to allow this.  Any extra images are also added to the end as described
under
.BR \-boot .
(Make sure you understand all this.)
.SP
The device need not be mounted when
.B installboot
is run, nor does it matter if it is.
.SP
.B Installboot
needs to be run again if
.I boot
is rewritten, because it will then occupy a new place on the disk.
.SP
Old boot parameters are kept if there are no images added.
.RE
.PP
.B \-b(oot)
.I device bootblock boot
.RI [ label :] image
\&...
.RS
This option fills a blank floppy in
.I device
with boot code and kernel images.  This "boot disk" does not have a root
file system, only the boot monitor and Minix kernels.  The boot parameters
sector is filled with code that enables menu options for selecting an
image.  After loading an image, the monitor will ask you to insert a root
file system diskette before starting Minix.
.SP
The labels used on the images should match those on the executables used
inside the image.  You can put a comma separated list of labels on an image
for each label used within the image.  For the image created earlier one
would create a boot floppy like this:
.SP
.RS
.nf
.BI "installboot \-b /dev/fd0 bootblock boot" " AT,XT:image"
.fi
.RE
.SP
If a label-list is omitted on an image, then that image will be selected by
default.  (Like in the normal one image, no labels case.)
.SP
Note that
.B \-device
and
.B \-boot
together allow you to make a boot floppy with or without a root file system.
With the boot code in the file system, attached to the end of it, or after
the boot block.  And with one or more kernel images in the file system or
at the end of the device.  Somewhat confusing.
.RE
.PP
.B \-m(aster)
.RI [ fix ]
.I device masterboot
.RS
This option installs the
.I masterboot
program into the boot sector of the given device.  If another device is
given instead of
.I masterboot
then its bootstrap code is copied to
.IR device .
The master bootstrap on a hard disk boots the active partition on that disk
at boot time.  The MS-DOS fdisk command normally puts a master bootstrap on
the hard disk.  Minix has two bootstraps that can be used as a master
bootstrap.  A fairly normal one named
.B masterboot
that works as follows:
.RS
.SP
If the ALT key is held down while booting then '/dev/hd?' appears and you
are expected to type a number key (0 \- 9) to select the device to boot.
.SP
If
.I fix
(a small number) is given then the bootstrap is locked into booting the
.BI /dev/hd fix
disk or primary partition.  This is needed if 'boot *hd\fIN\fP' is used from
the monitor to boot an O.S. that needs the active flag set.
.SP
If installed on a Minix floppy then it will try to boot the next floppy or
the first hard disk.  Ideal for floppies with just data on it, they will no
longer obstruct the boot process if left in the drive.  Also a very useful
trick to boot from floppy drive 1.
.SP
If installed on a hard disk then the active partition is selected and booted
as usual, unless none of the partitions is marked active, then it will boot
the next disk.  The latter is useful if you want to boot an operating
system from the second disk by default.
.RE
.SP
The second bootstrap is named
.BR extboot .
It has only one function, to boot the logical partition named by
.IR fix .
.I Fix
is not optional for
.B extboot
and must be a number-letter pair, like
.B 2c
for
.BR /dev/hd2c .
.SP
.B Extboot
or
.B masterboot
with a fix key need not be installed in the hard disk master bootstrap per
se if you don't want to mess with the DOS master bootstrap, or if you want
keep the active flag functioning.  An extended partition or a non-root Minix
partition are better candidates.  It seems logical to put
.B extboot
in the extended partition boot block.
.SP
A backup copy of the current master bootstrap (including the partition
table) can be made with:
.RS
.SP
dd if=\fIdevice\fP of=\fIbackup-file\fP count=1
.SP
.RE
A simple 'cat \fIbackup-file\fP > \fIdevice\fP' will put it back.  You can
also use
.B fdisk /mbr
under MS-DOS 5.0 (or newer) to restore the master bootstrap.
.RE
.RE
.SH FILES
.TP 25
.B /usr/mdec/bootblock
Minix bootstrap for the Minix root device.  To be placed in the boot sector.
.TP
.B /usr/mdec/boot
Minix Boot Monitor.  Can usually be found in the root directory of a bootable
device.
.TP
.B /usr/mdec/masterboot
Master bootstrap.  Can be placed in the first sector of a disk to select the
active partition.  In a Minix primary partition it selects the active
subpartition.
.TP
.B /usr/mdec/extboot
Extended partition bootstrap.
.SH "SEE ALSO"
.BR part (8),
.BR monitor (8).
.SH DIAGNOSTICS
.I Boot
doesn't fit on
.I device
.RS
If there is no space on the device to add the boot code.  This usually
means that there is no boot code in the file system you use
.B installboot \-device
on.
.RE
.PP
.I Image
doesn't fit on
.I device
.RS
If the device is too small for all the images you try to put on it.
.SH BUGS
It has four more options than the SunOS installboot program it is modeled
after.
.PP
The bootblock code has been crunched to such ugliness that you can use it
to scare little kids out of your garden.
.SH AUTHOR
Kees J. Bot ([e-mail])