usage(8)
NAME
usage - installing and using Minix
DESCRIPTION
This manual page describes the installation and use of Minix from a
System Administrators point of view. It contains an installation guide,
instructions on how to do the initial configuration and some other info.
Please read this document entirely before attempting to install Minix.
The installation steps are in the proper order, but not all the
information you may need is presented at the right moment. Other
detailed information that may be useful can be found in boot(8) and
hier(7).
1. REQUIREMENTS
The minimum system Minix can be installed on comfortably is an IBM PC/AT
or PS/2 with a 286 processor, 2 Mb memory, a 720 kb diskette drive, and
30 Mb free space on an AT, ESDI, or SCSI hard disk (the latter controlled
by an Adaptec 1540.) Minix for the 386 (Minix-386 for short) can be
installed on a machine with at least a 386sx processor and 3 Mb memory.
2. MINIX INSTALLATION BACKGROUND
The objective of the installation is to create a partition on your disk
and to put Minix into it. Minix really requires two partitions however,
so the single "primary" partition is split into two subpartitions. The a
subpartition will contain the root file system, and the c subpartition
will contain the /usr file system. What MS-DOS calls "drives", i.e C:,
D:, E:, Minix calls "file systems". Minix does not use drive letters,
but requires that one file system is made a part of another file system
by "mounting" one on the other. The "root" file system is always present
and starts with the directory "/", the root of the directory tree. The
root file system contains a few programs in /bin, device files in /dev,
and configuration files in /etc. This is just enough to get the system
started. Minix will soon extend its directory tree by mounting a file
system on the /usr directory. What is henceforth known as the /usr file
system contains all Minix programs in /usr/bin, file system sources in
/usr/src, etc, etc. The ROOT image contains the complete Minix root file
system, but USR contains just a small subset of the /usr file system,
with just enough utilities to install Minix. The complete /usr file
system is split up into the USR.TAZ, SYS.TAZ and CMD.TAZ archives that
are installed later to fill /usr.
Let's suppose your first hard disk, which has device name /dev/hd0, has
MS-DOS already present in the first primary partition (/dev/hd1), and
some free space left after that. After Minix is installed in that free
space the disk will look like this:
/dev/hd0 Whole hard disk #0
/dev/hd1 MS-DOS C: drive
/dev/hd2 Minix primary partition
/dev/hd2a Minix root partition
/dev/hd2c Minix /usr partition
/dev/hd0 is the sum of a partition table, /dev/hd1 and /dev/hd2.
Likewise is /dev/hd2 the sum of a subpartition table, /dev/hd2a and
/dev/hd2c. Read the "DEVICES" sections for more information on Minix
devices.
3. INSTALLATION
You can install Minix automatically or manually as described the sections
below. The end result is the same, but manual installation allows one to
deviate from the preconfigured choices. You may wish to read the manual
pages of the programs used below before you start. You may especially
want to read boot(8) if your machine is different from what the majority
buys, because you may need to set a few boot parameters to configure
drivers. To do this type ESC to get to the Boot Monitor prompt, set the
appropriate variables, use save to store the settings and menu to
continue where you left off.
To install the system you need two diskettes: a bootable root diskette
and a diskette full of binaries to use as /usr. These diskettes are
named ROOT and USR. These two diskettes may also be combined on a single
high density diskette. In that case the USR part is on the c partition.
Insert the ROOT diskette, boot the machine and type '=' to the menu. The
Minix kernel is loaded and takes control when you see the copyright
banner. After loading the root diskette into the RAM disk you will be
asked to finish the name of the device to mount on /usr. Type fd0c for a
diskette that contains both ROOT and USR, otherwise replace ROOT by USR
and type fd0. Login as root.
4. AUTOMATIC INSTALLATION
Type setup to start the installation script. First it offers to install
a national keyboard map. The names should be clear, except for us-swap,
which swaps the CTRL and CAPS LOCK keys of a standard US style keyboard
for people who believe that the natural place of CTRL is next to A. The
default suggested between [ and ] is the US standard keyboard.
The next thing to do is to make a partition, for this you are placed in a
partition table editor named part. This partition table editor is very
easy to use (in the author's opinion), but you will probably hate it.
You can move all over the place with the arrow keys, change values, and
make a mess of your partition table real quick. So if you get into
trouble, type 'q' to quit, 'n' to not write the table, and RETURN to
start over. Use the '?' key to get help.
With the '+' and '-' keys you can select the disk device to install on,
probably /dev/hd0, the first hard disk. Type 'r' to load the partition
table of the selected disk. Either create one new partition by modifying
a partition marked "None", or reuse an existing partition by changing its
type to "MINIX" (hex code 81). The FIPS program can be used under MS-DOS
to shrink an MS-DOS partition. FIPS splits the DOS partition in two, so
one of the two can be used for Minix. You have to be absolutely sure
which one. When in doubt, first use the FDISK program under DOS to
delete the extra partition, and let Minix part create a new one. DO NOT
use part to shrink an existing partition! Minix needs a partition of at
least 20 Mb, but not larger than 128 Mb (Minix-86) or 1 Gb (Minix-386).
The system needs 30 Mb in compiled state.
The script then wants to know the name of the partition you've created,
this name is probably still visible on the screen (hd2, hd6, something
like that.) The new partition table is reloaded into the disk driver,
and the new Minix partition is carved up into two subpartitions, a 1440
kb root and the rest for /usr.
After making /usr, it is immediately put to use to replace the
installation /usr file system so that you can remove the USR diskette and
insert the ROOT diskette (unless they are one and the same). The root
file system is filled with the contents of the ROOT diskette and slightly
patched up to work on the hard disk (/etc/fstab.)
To compute the size of the so-called "second level block cache" you are
asked to specify the RAM size of your machine. If you have plenty, i.e 4
Mb or more then simply hit RETURN, otherwise enter the size of your
system RAM in kilobytes.
You can now skip the next section and move to "TESTING", but it may be
instructive to read it anyway.
5. MANUAL INSTALLATION
The instructions that follow are at a very low level and require you to
be very careful. The big advantage is that you know precisely what tools
have been used and how everything works. The disadvantage is that you
may easily make a mistake that either forces you to start over if you are
lucky, or wipes out the contents of your hard disk if you are not. Only
if you really want to do something different should you use a manual
installation. Slavishly following the steps shown below will only make
you end up with the same result as an automatic installation.
Run part to make partitions to load the system into. The best thing to
do is to make one large primary partition of type "MINIX" and to carve
this partition up into three subpartitions for root and /usr. The
assumption is that you will use the second partition on the first hard
disk, /dev/hd2, and that hd2a is the root subpartition and hd2c is /usr.
If you want to use the first partition on the second hard disk for
instance, then substitute hd6 and hd6[ac] for the above. On a SCSI disk
it will be /dev/sd2 for the second partition on the disk at target 0.
See the section on devices below, and the manual pages of part(8), hd(4),
and sd(4). Start part and select the whole hard disk device (the
"multiple of 5" device) that you want to install Minix onto. In our
example it will be /dev/hd0.
Use part to make a single partition in the primary partition table of
type "MINIX", then hit '>' on this new partition to make a subpartition
table.
For the root subpartition you are advised to use 1440 kb exactly. You
can make it larger if you want to, but it is advisable never to let the
contents outgrow a floppy. (The ROOT diskette is a copy of a root file
system, and will be used to fill your root subpartition.)
The second subpartition is either empty or a "scratch" partition. Minix
no longer uses the b subpartition for anything useful anymore, but it has
become customary to have root on a and /usr on c. (You are free to
ignore this convention, of course.)
Use the rest of the partition for the /usr c subpartition.
When you are done check that /dev/hd2a is active (the * after the
partition number) so you can boot from it later.
If your disk has bad blocks then don't put the root or scratch
subpartition on top of them. Make sure the inode tables in the other
partitions don't have bad blocks either. You can put the subpartitions
out of order on the disk if that helps. Subpartition tables, other than
the main partition table, are not sorted by the driver.
After making the partitions you do not have to reboot. The disk driver
reloads the partition tables on the next access if the disk is not in
use. (Open or mounted.)
To be able to boot from /dev/hd2a you must place a master bootstrap in
/dev/hd2. It has been placed there by part if it told you that it was
creating a new partition table, but
installboot -m /dev/hd2 /usr/mdec/masterboot
will put it there for sure.
You will start by making a file system for /usr and filling it partially.
This may seem to be out of order, but you can't insert the ROOT floppy
right now.
mkfs /dev/hd2c
readall -b /dev/hd2c | sh
mount /dev/hd2c /mnt
cpdir -v /usr /mnt
This will create a file system on /dev/hd2c, mount it on /mnt, and copy
the contents of the USR floppy onto it. The call to readall marks bad
blocks on the file system as unusable, you can omit this on a drive known
to be spotless (IDE or SCSI.)
You can now use the new /usr in place of the USR floppy:
umount /dev/hd2c
umount /dev/fd0 # fd0c if combined
mount /dev/hd2c /usr
This little dance has freed up your floppy drive, so please remove the
USR diskette and replace it by the ROOT diskette. Make a file system for
the root with at least 512 inodes (files), and fill it from the floppy:
mkfs -i 512 /dev/hd2a
mount /dev/fd0 /fd0
mount /dev/hd2a /mnt
cpdir -v /fd0 /mnt
umount /dev/fd0
Remove /mnt/etc/issue to get rid of the "use setup" message that greets
you when you boot, and edit the file /mnt/etc/fstab to name the devices
Minix has been installed on. In our example it should look like this:
root=/dev/hd2a
usr=/dev/hd2c
Unmount the new root:
umount /dev/hd2a
Make it bootable:
installboot -d /dev/hd2a /usr/mdec/bootblock boot
The automatic script would now set the rootdev and ramimagedev boot
variables. You can do this now using the edparams command, but it is
easier to postpone it until the testing phase. The settings should be:
rootdev=hd2a
ramimagedev=hd2a
6. TESTING
By now a new Minix system is present on your hard disk. Time to see if
it works. Leave the ROOT diskette in the drive and type halt. You are
now going to use the power of the Boot Monitor on the diskette to boot
the Minix partition on the hard disk. Use the monitor command boot hd2
to boot the primary partition Minix has been installed in. (It is "hd2"
in our example.) For a SCSI disk you will have to use a 'hd' name too.
The monitor uses the BIOS, so you will have to treat it as a "normal"
disk at this point.
The hard disk bootstrap is now showing the menu again. You can type '='
to start Minix, but you probably want to change the boot parameters. Hit
ESC once more to get to the command prompt. The command set shows what
the current parameters are. Here is an example that shows how to make a
menu to either start Minix or boot MS-DOS:
minix(=,Minix) {boot}
dos(d,MS-DOS) {boot hd1}
save
MS-DOS is assumed to be in the first partition in the example above
(hd1). When finished type menu to see if the menu looks right. If so
hit '=' to start Minix.
7. ADDING PROGRAMS AND SOURCES TO /usr
The setup command can also be used to add files from floppy sets to the
system. The USR.TAZ (programs and stuff), SYS.TAZ (system sources), and
CMD.TAZ (commands sources) are all installed relative to the /usr
directory, so the command to use three times is
setup /usr
Setup will ask for the size of data on the floppies, which is by default
simply the entire floppy. Don't worry if you see a few "File exists"
errors while extracting, as some directories already exist. You need the
USR.TAZ set if you want a working Minix system, SYS.TAZ if you want
recompile the system or study it, and CMD.TAZ if you also want the
sources of the simple commands. On a disk space starved machine you
could opt to do without the commands sources, as they are not absolutely
necessary to understand Minix.
If your machine does not have enough memory to run setup /usr then type
these commands manually:
cd /usr
vol /dev/fd0 | uncompress | tar xvfp -
8. NAMES
A standalone machine will have to be given a name. As root type
echo name >/etc/hostname.file
to change the host name of your machine to name.
9. ACTIVE ON BOOT
You may want to make the Minix partition active so that it is
automatically booted. With DOS fdisk or Minix part, mark the primary
partition that contains Minix active. Using the menu you made earlier
you can boot either Minix or DOS at a keypress. You can even set
timeouts. To boot Minix automatically after 5 seconds:
main() {trap 5000 minix; menu}
See monitor(8) for all the details on the monitor.
If you don't trust this then you can rig up a diskette that boots the
Minix partition when left in the drive:
installboot -m 2 /dev/fd0 /usr/mdec/masterboot
The number 2 indicates the hard disk partition that must be booted, you
can use the numbers 1 to 9 for hd1 to hd9.
10. DEVICES
A crash course on the Minix devices in /dev: The two hard disks are
named hd0 and hd5. These "multiple of five" devices address the entire
hard disk, from the first to the last byte. Each disk has four
partitions, for disk 0 they are hd1, hd2, hd3, and hd4. And for disk 1
they are named hd6, hd7, hd8, and hd9. These partitions may contain file
systems, hd1 often contains the MS-DOS "C:" file system. Minix can use
these partitions for file systems too, but you can also partition one of
these "primary partitions" into four so-called "subpartitions". The
subpartitions of hd1 are named hd1a, hd1b, hd1c, and hd1d. The other
partitions may have four subpartitions that are named in the same way by
adding a letter from a to d. So one disk may have four partitions, and
16 subpartititions total. SCSI disks are named in the same way, from sd0
to sd39d for all possible devices for all eight SCSI targets. The two
floppy disks are fd0 and fd1. Each may have four partitions named fd0a,
fd0b, ... fd1d. The command MAKEDEV knows how to make devices, and
DESCRIBE can tell you what an unknown device may be, or even what all
devices in /dev may be if called without arguments. Devices are
described fully in dev(4), and in the device specific manual pages like
fd(4) and hd(4).
11. EDITORS
The editors available are elvis (a vi clone), elle (a simple emacs
clone), and the old Minix mined editor. Of these editors only elvis can
recover your file after a system crash. Only mined is available at
installation time. (All you need to know about mined right now is that
CTRL-X gets you out of it.)
12. INSTALLING ON A SCSI DISK
Using a disk other than a hd disk complicates things a bit. The Boot
Monitor uses the BIOS, so it names all disks with hd names. So it is
boot hd1 to boot partition 1, and ramimagedev=sd2a to tell Minix its root
partition. If you have both a normal and a SCSI disk then the disks may
be hd0 and hd5 to the Monitor, and hd0 and sd0 to Minix.
13. NATIONAL KEYBOARDS
The directory /usr/lib/keymaps contains keymap tables for several
national keyboards. If you have a German keyboard for instance, then
loadkeys /usr/lib/keymaps/german.map
will load the German key translation table into the keyboard driver.
Copy the map to /etc/keymap once Minix is installed on the hard disk,
because having to type a key sequence like one of these:
loadkezs -usr-lib-kezmaps-german.map
loqdkeys =usr=lib=key,qps=french.,qp
on a reboot gets a bit annoying after a while. Send corrections and new
keymaps to the person named below. (Do not send a Dutch keymap, buy
yourself a real keyboard instead.)
SUGGESTIONS
Below are a few useful suggestions. Some of the information can be of
use in other situations than described here.
14. VIRTUAL CONSOLES
Hold down the ALT key and press the left or right arrow key, F1, or F2.
This switches the console between two login sessions. (Unless you have
an old mono adapter, because virtual consoles sit in video memory, and a
mono adapter only has memory for one.)
Note that kernel messages, including function key output, only appear on
the first console. This may be confusing, but it keeps the other
consoles clean.
15. LOW ON MEMORY
The normal installation requires that you have enough memory for a large
RAM disk. You can still install Minix normally if you either have a high
density diskette drive for a combined root+usr floppy, or you have two
floppy drives of at least 720 kb. Before booting you have to set the
variable rootdev to the same value as ramimagedev. This is slower then a
RAM disk, but saves a lot of memory.
The automatic installation script knows how to handle this new situation.
If you install manually then you have to use
cpdir -vx / /mnt
to copy the root device to disk. When it is time to fill /usr and you
only have one floppy drive then hit DEL to get out of the installation
script and reboot as described in "TESTING". You can then finish the
installation manually.
16. LOW ON MEMORY AND ONLY ONE 720 KB FLOPPY DRIVE
If you only have one 720 kb floppy drive and your system is low on memory
then you can use the TINYROOT boot image. This image contains a small
kernel with only the BIOS disk driver, and a small root file system. You
can use this disk to boot your machine. Use the normal ROOT to install
the root file system. Keep booting your machine with TINYROOT until you
have compiled a small kernel for your system. Use the rootdev boot
variable to select the hard disk root file system. Do not use TINYROOT
for anything other than booting, always use ROOT when mentioned.
17. FLOPPY DRIVE 1 IS A HIGH DENSITY DRIVE
If you would like to install from floppy drive 1 then you need to copy at
least one sector from the USR image onto a diskette for drive 0. The USR
bootstrap has been rigged to boot the other drive.
18. INSTALLING ON A SECOND HARD DISK
Minix doesn't care if it is installed on the second disk of a system with
two disks. The only problem is to get it booted. You can either rig up
a diskette to boot Minix as shown earlier, or you can use the same trick
on the first disk. The command
installboot -m 5 /dev/hd0 /usr/mdec/masterboot
will lock the first disk into booting the second disk. Note that this
command modifies the disk outside a Minix partition, overwriting a bit of
code that has likely been put there by DOS fdisk. First verify that the
Boot Monitor can boot a DOS partition, because then the Minix master
bootstrap can do it too.
19. LOTS OF MEMORY ON A 286
You will have a hard time making Minix run out of 3 Mb memory. Memory
you can spare can be used for a "second level block cache" on the RAM
disk. The File System uses the second level cache to store copies of
disk blocks that are pushed out of the normal (primary) block cache. The
size of the primary cache is compiled into the FS server, but the size of
the second level cache can be set with the ramsize boot variable. Set it
to a number between 0 and 512. 512 kilobytes is enough to keep most of
the compiler cached.
20. LOTS OF MEMORY ON A 386+
Processes can be as big as you'd like on a 386, but in practice 4 Mb is
nice. The installation script sets up a second level cache for Minix-386
of up to 1024 kilobytes. This is because the default file system cache
is only 80 kb. Your first point of call is to get rid of the poorly
performing second level cache and to assign the memory used by it to the
normal block cache by enlarging the appropriate NR_BUFS and NR_BUF_HASH
constants in <minix/config.h> with as much as you can spare. (1024 for
NR_BUFS is the minimum to keep cc -c cached. 2048 is then a nice value
for NR_BUF_HASH.) Disable the second level cache, compile a new kernel,
reboot and set ramsize to 0.
21. LOTS OF DISK SPACE
The maximum file system size is 1 Gb for Minix-386 and 128 Mb for Minix-
86. (Minix-86 can handle larger file systems, but fsck can't check
them.) Note that a Minix file system can only contain 65535 inodes
(files), so the average file should be 16 kb to completely fill it. It
may be better to make two smaller file systems. Besides, fsck takes
forever on a large file system.
SYSTEM ADMINISTRATION
The system has been set up with the idea that working as root is a bad
thing to do. As root you are in no way protected from doing stupid
things. So don't do development as root, but work as bin! Only in
exceptional cases do you want to become root. Being root is fun for
wannabe hackers; administrators know better.
To make life easier for bin, some programs like su(1), install(1) and
shutdown(8) treat bin and other members of the operator group as special
and allow them the privileges of root. (One is an operator if one's
group id is zero.) Operators should share the shadow password of root by
having ##root in their password field. This way they all have one face
(password) to the outside world, forming no greater security risk than
root alone.
The home directory of bin contains one important Makefile. You can use
it to recompile all the commands and libraries of the system. Type make
to see the usage message. If you want to compile just one command then
you can simply type make to do so. To put it in its proper place you
have to type make install. Read the Makefiles in the commands and lib
subdirectories to understand how everything is put together. If you are
tight on memory then make may fail to traverse down the source tree and
also compile things. You will have to type make in each subdirectory.
You can run make in /usr/src at the end to see if you've missed something
or not.
The login shell of bin is ash, the BSD shell. It has been modified to
offer simple line editing using the editline(3) library. Ash is rather
big, so you may have to change bin's shell back to /bin/sh with chsh(1)
if you are low on memory. Do not change root's shell to ash, and do not
replace /bin/sh by ash. It may run out of memory at the wrong moment.
The kernel is not compiled from the master Makefile. To make a new
kernel you have to step into the tools directory. There you can run four
different make commands:
make This makes all the different kernel parts and combines them in the
file named image.
make fdboot
As above and then makes a boot floppy that you can use to restart
your system with. You are prompted for the floppy device name.
make hdboot
First makes the image file and then copies it into the directory
/minix. If there are already two images in that directory then the
newest image will be removed to make space for this newer image. It
is assumed that the oldest image is the most stable system image,
one that always works, and that the newest image is experimental.
Check beforehand what /minix contains before you run make hdboot.
Remove the oldest image if you want another image to become the
stable image. The Boot Monitor chooses the newest image in /minix
to boot. You can use the monitor command ls minix to view the
images present, and set the image variable to the full name of the
image you want to use instead if the newest doesn't work. The
images in /minix are named using the Minix release and version
numbers with an extra revision number added to distinguish the
images.
The first new kernel you would like to make is one configured for your
system. The kernel you are running now contains several hard disk
drivers you don't need, and it does not have a TCP/IP server that you may
want to have. In <minix/config.h> you can find a number of ENABLE_XXX
variables that can be set to 0 to exclude, or 1 to include a particular
driver. Another driver related variable is DMA_SECTORS. This variable
sets the size of a buffer used by DMA based disk drivers (all but the
floppy, AT/IDE, and Adaptec drivers). Raise its value to greatly improve
throughput, especially writing. A value of 16 shows good results. (The
BIOS driver benefits most, because it is a long way to the BIOS from
protected mode, especially from 286 protected mode.) You can increase
NR_CONS if you want to have more virtual consoles. Having more consoles
costs little memory, because all the consoles are kept in video memory.
Scrolling speed of the console will go down if more virtual consoles
share the available memory. CGA cards have space for 4 consoles, EGA and
VGA can have 8 consoles. The NR_PTYS variable sets the number of pseudo-
ttys. You need pseudo-ttys to be able to login remotely over a network
with the rlogin command. Each remote login session needs one pseudo-tty.
If you fear that the system will now run out of processes then increase
NR_PROCS. Configuring a new kernel is sometimes not enough to enable new
devices, you sometimes need to use the MAKEDEV command to make new device
files in /dev. For pseudo-ttys you also have to check if /etc/ttytab
mentiones the new devices.
New additions to the system can be made in the /usr/local tree. An empty
directory tree has been set up for you and binaries and manual pages are
already in the search paths. You can make a new user entry with the
adduser command.
The TZ variable in /etc/profile tells the time zone offset from the wall
clock time to GMT. You have to change it for your time zone. (See
TZ(5).)
The function keys produce debug dumps, showing various interesting data
about the system. F1 lists processes and F5 shows ethernet stats, which
may be of use now. Read console(4) to know all the details of the screen
and keyboard.
22. SYSTEM SHUTDOWN
You can't just turn a Minix system off. Minix must be told to flush the
modified data in the file system cache first. The following
commands/keystrokes can be used to exit Minix properly:
shutdown
First alert all users and then all processes of the impending
shutdown then halt or reboot the system in one of various ways. See
shutdown(8).
reboot / halt
Alert all processes of the system shutdown then reboot or halt.
CTRL-ALT-DEL
Halt the system by running shutdown -h now.
Minix halts by returning to the Boot Monitor, Minix reboots by
instructing the monitor to reboot Minix. (Minix is just a subprocess to
the monitor.) Either halt Minix and use monitor commands to escape
Minix, or use shutdown -R to reset the system.
FILES
/usr/ast Honorary home directory of Andew S. Tanenbaum. Doubles as
the place where the default setup for a new user is found.
SEE ALSO
monitor(8), boot(8), part(8), mkfs(1), mount(8), M(8), fstab(5), hier(7),
console(4), dev(4), adduser(8), TZ(5), mkdist(8), shutdown(8).
"Operating Systems - Design and Implementation" by Andrew S. Tanenbaum.
NOTES
The notation <file.h> refers to a C language include file in
/usr/include.
Root and bin do not have the current directory in their program search
path to avoid executing programs left around by malicious people. This
means that to run foo from the current directory, ./foo must be typed.
Some of the commands have changed since earlier Minix versions. For
instance mkfs doesn't need a size argument anymore, and vol automagically
determines if it needs to read or write. Keep this in mind if you use an
older Minix version to examine the newer system.
BUGS
There are many PS/2 models, all different. Some will run Minix, some
won't, some crippled if you lie to Minix by setting processor to 86.
Almost no PS/2 has a standard disk, so setting hd to esdi or bios will be
necessary.
While testing a full library rebuild of this distribution it sometimes
happened that some things were not put back into the library. This seems
to be fixed, but we do not understand why the fix fixed the problem. So
if you see strange "undefined" errors when compiling a program after a
library rebuild then run make install again in /usr/src/lib/ to try and
add the missing pieces.
Except for the floppy driver none of the DMA based drivers know about DMA
being limited to a 24 bits address, i.e. the first 16 Mb. So under
Minix-386 you run a slight risk that a tar or dd command may use a buffer
above 16 Mb for reading or writing to a character device. This only
happens if the low 16 Mb is taken by some huge processes, and you have
more than 16 Mb, of course.
AUTHOR
Kees J. Bot (kjb@cs.vu.nl)