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NAME
monitor, edparams - load and start Minix, modify boot
parameters
SYNOPSIS
edparams device [command ...]
boot.com virdisk
DESCRIPTION
This text describes the Boot Monitor, a boot time
interactive program designed not only to load and start
Minix, its most important task, but to also provide an easy
to use interface to configure Minix and to boot other
operating systems.
The monitor is controlled with an environment that is
modeled after the Bourne shell. This environment is filled
at startup with default values that depend on the machine
the monitor is running on and the environment settings saved
into the boot parameters sector (the second sector on a
device). When the environment is loaded, the monitor
executes the function named main, which by default starts a
simple menu.
The environment can be manipulated at boot time from the
monitor prompt, but may also be edited using edparams on a
given device. Edparams simulates the monitor as much as it
can, echoing commands it can't execute between brackets. It
can also be used in Makefiles and scripts by giving it
commands as arguments.
The MS-DOS version of the monitor, usually named boot.com
under DOS, boots Minix from a "DOS virtual disk". (See
below.)
COMMANDS
The monitor is best described by the commands you can type
to the '>' prompt. This is known as the "monitor mode".
You can enter this mode by hitting the Escape key. These
are the monitor commands:
name = [device] value
Set environment variable.
Changes the value of name to value. The optional word
device marks name as being subject to device
translation. (See the section on devices.) These
(name, value) pairs are passed to the kernel who uses
them to configure itself. These variables are passed
by default:
rootdev
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This is the device used as your root device. It
is by default set to ram, which means that the
device specified by ramimagedev will be loaded
into the RAM disk and used as root. If you change
this variable then a physical device will be used
as root, and the RAM disk will be uninitialized
and have the size specified by ramsize.
ramimagedev
Describes the device to use to initialize the RAM
disk if rootdev is set to ram. It's by default
set to bootdev, a special name for the device the
monitor booted from.
ramsize
The size of the RAM disk. If the RAM disk is used
for the root file system then the root file system
is stretched out to ramsize if possible.
processor
Set by default to 86, 186, 286, 386, 486, ...
depending on the hardware you have. You can set
it to a smaller value to test your kernel in a
more limited environment.
bus
The type of system bus, either xt, at or mca.
This answers basic questions like: "How many
interrupt controllers and how to initialize?" Or:
"Does the keyboard have LEDs?"
memsize
Kilobytes of conventional memory. This is the
amount of RAM within the first megabyte.
emssize
Kilobytes of extended memory.
video
Describes capabilities of the VDU: mda, cga, ega
or vga.
chrome
Either color or mono.
console
If set to a hexadecimal value makes the monitor
set the BIOS video mode to this value. This
allows the use of video modes with more rows or
colums than the standard 80x25 mode. The kernel
must of course be able to handle a nonstandard
mode. More parameters may follow the mode number.
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Warning: Not all monitors can handle all of the
modes, some may generate frequencies that can
damage your monitor. Read the manual of card and
monitor for details.
Two variables are only used by the monitor, even though
they are passed to the kernel too:
image
The name of the file containing the kernel image,
by default minix. If it refers to a directory
however then the newest file inside the directory
is chosen to be the kernel image. The names
inside /minix/ are best set to the Minix version
you are using, which looks good when the monitor
prints its name. Rules for pretty printing image
names:
A '/' or '_' is changed to a space.
The first letter is changed from lowercase to
uppercase.
An 'r' if followed by a digit changes to "
revision ".
label
If set then only processes marked with this label
or without a label are loaded from the image.
Installboot -boot will create functions to select
images and labels. These functions will set label and
image and echo what you selected. The two numbers
separated by a colon used as an image name tell the
starting sector and sector count of the image on disk.
name() { ... }
Define function.
Functions may be used to bundle a set of commands, so
that you can easily boot Minix with a different set of
parameters then normal. E.g.
ram() { rootdev=ram; boot }
will allow you to run Minix with the root device on RAM
for a change, if you normally use a real device as
root. The only pre-set function is main with default
value menu, which is the default command executed by
the monitor. You can use newlines after the ')' token,
the monitor will then use a '+' prompt and ask for the
rest.
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name(key) { ... }
Define kernel selecting function.
The menu command uses functions like these to add menu
entries to select a different kernel from a boot disk.
Installboot -boot produces these functions when the
images are labeled. The label AT would give:
AT(a) {label=AT;image=42:626;echo AT kernel
selected;menu}
With the menu option:
a Select AT kernel
Typing a will then execute the AT function above.
name(key,text) { ... }
User defined menu option.
This variant may be used to make any menu entry you
like:
dos(d,Boot MS-DOS) { boot hd1 }
Text may be anything, even parentheses if they match.
name
Call function.
If name is a user defined function then its value is
expanded and executed in place of name. Try a
recursive one like 'rec() {rec;xx}' one day. You can
see the monitor run out of space with nice messages
about using chmem(1) to increase it's heap.
boot [-opts]
boot device
Boot Minix or another O.S.
Without an argument, boot will load and execute the
Minix image named by the image variable. With options
the variable bootopts is first set to -opts before
Minix is started, and unset when Minix returns. With a
device argument, boot loads the boot sector of device
into memory and jumps to it, starting another operating
system. You would normally use partitions on the first
hard disk for this command (hd[1-4]), using hd0 will
also work (choosing the active partition). One can
also boot devices on the second hard disk (hd[5-9]) if
the bootstrap writer did not hardwire the disk number
to disk 0.
Some Operating Systems can only be booted from the
active partition, if you use a '*', e.g. boot *hd3,
then partition 3 is first made active. You'll then
need to use installboot -master with a fix key to
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forcefully boot the Minix partition at startup.
delay [msec]
Delay (500 msec default).
Fast booting speed was one of the objectives when this
program was created, so a hard disk boot usually takes
only a fraction of a second. If you need some time (to
hit Escape, or stare at the numbers) you can use delay
to make the monitor pause for a specified amount of
time. To specify a delay just before Minix is started,
you can set the variable delay to a number of
milliseconds. Example:
main() {delay 250; delay=500; boot}
Look at this carefully, 'delay 250' means: "wait 1/4
sec now!", while 'delay=500' means: "wait 1/2 sec after
loading Minix".
If you use delay=swap then the monitor will wait until
you have inserted a root diskette and typed RETURN.
echo word ...
Print these words.
Used to tell you that you just selected image X.
ls [directory]
List contents of a directory.
Useful when looking for kernel images.
menu
Menu driven startup.
This command allows you to execute functions defined
with a key. If no menu functions have been defined
then menu will use this one hidden built-in function:
*(=,Start Minix) { boot }
Kernel selecting functions only add new options to this
set, but if you define a two argument function yourself
then the above one is no longer shown, allowing you to
customize the menu completely. Your first function
definition should therefore be one that starts Minix.
Menu entries are shown in the same order as set shows
them. If you don't like the order then you have to
unset the functions and retype them in the proper
order.
If you type a key then a scheduled trap is killed and
the appropriate menu function is executed. If you need
more time to choose then hit the spacebar. A key not
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on the menu also kills a trap, but does nothing more.
save
Save environment.
This will save all the environment variables and
functions with nondefault values to the parameter
sector (the second sector on the boot device), so they
are automatically set the next time you boot the
monitor.
set
Show environment.
Show the current values of the environment variables
and functions. Default values are shown between
parentheses to distinguish them from values that were
explicitly set.
trap msec command
Schedule command.
Schedules a command to be executed after msec
milliseconds. Only the monitor mode cannot be
interrupted, a scheduled trap is killed when the prompt
is printed. Example:
main() {trap 10000 boot; menu}
This gives you 10 seconds to choose a menu option
before Minix is booted.
unset name ...
Unset environment variables.
Removes the named variables and functions from the
environment, and sets special variables back to their
default values. This is also the only way to remove
the "device name translation" property from a variable.
exit
Exit the monitor
Reboot the machine, exit to Minix or exit to DOS as
appropriate.
DEVICES
The Minix kernel can't do anything with device names, so
they have to be translated to device numbers before they are
passed to the kernel. This number is found under the
st_rdev field (see stat(2)) of the file on the boot file
system. The monitor will look for the device file with the
working directory set to '/dev'. If it can't find the
device name then it will translate names like 'ram', 'fd1',
'hd6', 'hd3a', and 'sd2' to what it itself thinks the
numbers should be.
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The special name bootdev is translated to the name of the
device booted from, like 'fd0', or 'hd3', and then searched
for in /dev. Bootdev can't be translated to a device other
then the fd or hd devices, so SCSI devices for instance must
be named explicitly.
EXTENSIONS
A few extensions have been made to this program for kernel
hackers. They may be triggered by setting bits in the flags
word in the kernel startup code (the mpx file.) The flag
bits are:
0x0001 Call kernel in 386 mode.
0x0002 Do not make space for the bss areas of processes
other then the kernel.
0x0004 Use the stack size set by chmem(1).
0x0008 Load MM, FS, etc. into extended memory.
0x0010 No need to patch process sizes into the kernel.
0x0020 The kernel can return to the monitor on halt or
reboot.
MS-DOS MONITOR
Minix-vmd has a version of the monitor that runs under MS-
DOS to boot a "DOS virtual disk". It is a simple COM
program that interprets an MS-DOS file as a disk, loads a
Minix kernel from the active partition in the same way as
the BIOS based monitor, and executes it to start Minix. All
the monitor commands function in the same way, except for
the boot command, it can only load Minix. The memory that
MS-DOS has in use is copied out of the way when Minix takes
control, and is put back in place when Minix exits. This
memory shuffling also happens when the BIOS disk driver
makes BIOS calls, slowing things to a crawl. It is better
to use a Minix driver. The MS-DOS monitor does not work if
there is a memory manager active that runs in 386 protected
mode, like EMM386.
SEE ALSO
chmem(1), stat(2), installboot(8), usage(8), boot(8).
BUGS
The delay command will hang forever on the original IBM PC
(not the XT!). Not that it matters, as everything takes
forever on that box.
Reading the first sector to boot a floppy (e.g. boot fd1),
is done using whatever floppy parameters boot currently has
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available. This will probably always work.
The two forms of delay are a crock.
The word emssize comes from EMS, that has to do with
expanded memory, not extended memory.
ACKNOWLEDGMENTS
Guy Helmer, for the floppy sensing code that somehow
disappeared into the boot block.
Earl Chew, for the inspiration his ShoeLace package
provided, unless he wants to file a "look and feel" suit
against me, then I will say I modeled it after the SunOS ROM
boot monitor, which is also true.
AUTHOR
Kees J. Bot (kjb@cs.vu.nl)
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