monitor(8)
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
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. 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.
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 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 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.
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.
0x0040 Offer generic BIOS support instead of just INT 13 (disk I/O).
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 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)