288 lines
10 KiB
Groff
288 lines
10 KiB
Groff
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.TH DOSMINIX 8
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.SH NAME
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dosminix, mkfile \- Running Minix under DOS
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.SH SYNOPSIS
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.RB "C:\eMINIX> " "boot disk0.mnx" "\0\0\0\0\0(Typical example)"
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.br
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.RB "C:\eMINIX> " "mkfile \fIsize disk"
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.SH DESCRIPTION
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.de SP
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.if t .sp 0.4
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.if n .sp
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..
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This text describes running Minix
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.\" or Minix-vmd
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under DOS. The DOS version
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of the Boot Monitor, described in
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.BR monitor (8),
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grabs as much memory as DOS is willing to give, loads Minix into that memory
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from the active partition of a "file as disk", and jumps to the Minix kernel
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to let Minix take control. As far as DOS is concerned Minix is just a part
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of the
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.B boot.com
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program.
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.PP
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In the example above
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.B disk0.mnx
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is the "file as disk". It is a file of many megabytes that is used by Minix
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as a disk of four partitions. These partitions will normally be
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.B /dev/dosd1
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through
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.BR /dev/dosd4 ,
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with
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.BR /dev/dosd0
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for the whole "disk". The Boot Monitor will set the
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.B dosd0
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boot variable to the name of the disk (its first argument), the root file
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system will be the active partition, usually
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.BR dosd1 .
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It is better to use the special name
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.B bootdev
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to indicate this device, usually in the setting
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.BR rootdev = bootdev .
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.PP
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Once Minix is running it will operate the same as if started from a regular
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disk partition until it is shut down. On shutdown from protected mode it
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will return to the Boot Monitor prompt, and with the
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.B exit
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command you leave the Boot Monitor and return to DOS. Shutting down from
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real mode will reboot the machine, just like when run from a disk partition.
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(This more or less crashes DOS, but DOS is used to such abuse.)
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.SS EMM386
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Minix can't run in protected mode (286 or 386 mode) if DOS is using a memory
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manager like
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.BR EMM386 .
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You can either temporarily comment out EMM386 from
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.BR CONFIG.SYS ,
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or you can press
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.B F8
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on startup to bypass CONFIG.SYS. This is only possible with the later DOS
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versions.
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.SS "Windows 95"
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Press F8 at startup to make the boot menu visible. Choose
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"\fBCommand prompt\fP", or "\fBSafe mode command prompt\fP" to run DOS.
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Use the "safe mode" if EMM386 is started in CONFIG.SYS.
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.PP
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Typing F8 at the right moment isn't easy, so you may want to change the way
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Windows boots by editing the
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.B MSDOS.SYS
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file found in the root directory of your Windows system. This is alas not
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trivial.
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Open a window on your main drive, click on "\fBView\fP" and choose
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"\fBOptions\fP." In the Options window choose "\fBView\fP" and enable
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"\fBShow all files\fP". The MSDOS.SYS file should now be visible, among
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several other hidden files. Right-click on the MSDOS.SYS icon, choose
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"\fBProperties\fP" and disable "\fBRead-only\fP". Bring MSDOS.SYS into a
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simple text editor such as Notepad. In the
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.B "[Options]"
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segment add the following lines (or change existing lines into):
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.PP
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.RS
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.nf
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BootMenu=2
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BootMenuDelay=5
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.fi
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.RE
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.PP
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The first setting makes the Windows boot menu always visible, and the second
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line changes the delay before booting to 5 seconds. Take care not to change
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anything else, or things will go horribly wrong. Save MSDOS.SYS and exit.
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Don't forget to make MSDOS.SYS read-only again, and also hide all the hidden
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files again, unless you like it this way.
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.SS "DOS compatibility box"
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The 16-bit version of standard Minix can be run in real mode in a DOS box.
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This is somewhat surprising, because it means Windows 95 simulates devices
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like the keyboard, timer, and interrupt controller well enough to fool Minix
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into thinking that all is well. Alas it doesn't work as well under Windows
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NT. Keypresses get lost if you type to fast, and using the floppy
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occasionally locks Minix up. This is a bit disappointing, because it is the
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only way to run Minix under NT. Under Windows 95 one is better off
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putting the system in DOS at boot and then to run Minix in protected mode.
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.PP
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One thing that is better under NT is that the Boot Monitor is able to get a
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so-called "Upper Memory Block", thereby raising useful memory to about 750K.
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Windows 95 however hogs leftover UMB memory in a process named
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.BR vmm32 ,
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whatever that may be. To get
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some of this memory you can put
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.B "BOOT /U"
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at the start of
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.BR autoexec.bat .
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The monitor will grab a 64K UMB if it can get it, and keep that memory safe
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for use by Minix when it is later started from Windows.
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.PP
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The easiest way to start Minix is to give all Minix disk files the suffix
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.BR MNX .
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Doubleclick on the disk you want to run to make the "\fBOpen With\fP" window
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appear. Click on "\fBOther\fP" and browse to the
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.B BOOT.COM
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program. Set the name of the .mnx files to "\fBMinix "disk" file\fP" in the
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description box if you want everything right. In the future you can
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just click on a Minix disk file to run it, you don't have to start a DOS
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box first. (To make it perfect use "View", "Options", "File Types", choose
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"Minix "disk" file", "Edit", "Change Icon", "Browse", select MINIX.ICO.)
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.PP
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When Minix shuts down it will try to reboot what it thinks is a PC. Windows
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seems to assume that the DOS session has exited. Right-click on the
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BOOT.COM program, "Properties", "Program", and enable "Close on exit" to make
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the DOS box disappear automatically when Minix thinks it reboots. You may
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also want to lock the font to
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.BR 7x12 ,
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or any other font that isn't ugly.
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.PP
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Minix disk files are opened in a write-exclusive mode. A second Minix
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session can only open it read-only, which may lead to a "can't open
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root device" error.
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.SS "Mkfile"
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Minix disk files can be created or resized with the
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.B mkfile
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utility. Its two arguments are the size and name of the disk file. The
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size is a number optionally followed by the letter
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.BR k ,
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.BR m
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or
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.BR g
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to specify kilobytes, megabytes, or even gigabytes. So the call
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.PP
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.RS
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.B "mkfile 50m disk5.mnx"
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.RE
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.PP
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will create a 50 megabyte file named
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.BR disk5.mnx .
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If the file already exist then it is shrunk or grown to 50 megabytes. No
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data is lost if the file is grown. If the file is shrunk then only the data
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that is cut off is lost. These features allow one to inrease the size of a
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Minix /usr partition with the following recipe:
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.PP
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.RS
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.ta +24n+2m
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.nf
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copy disk0.mnx disk0.new Copy the disk to disk0.new
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mkfile 100M disk0.new Enlarge to 100 megabytes
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boot disk0.mnx Boot the old "disk"
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[ESC] Get the attention of the monitor
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dosd5=disk0.new /dev/dosd5 becomes disk0.new
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boot
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\&...
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login: root
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.fi
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.in +(24n+2m)
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.ti -(24n+2m)
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part Choose dosd5, move to the Size field of dosd7
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partition, hit 'm' to fill it out to the end of the "disk". Write and quit.
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.in -(24n+2m)
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.nf
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mkfs /dev/dosd7 Recreate the file system, but larger
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mount /dev/dosd7 /mnt
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cpdir -v /usr /mnt Copy /usr to the new disk's /usr to be
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shutdown Back to the monitor
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exit Back to DOS
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ren disk0.mnx disk0.old
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ren disk0.new disk0.mnx Replace old by new
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boot disk0.mnx Run the larger system
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.fi
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.RE
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.PP
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Now Minix runs from a larger "disk". Don't worry if it claims to have
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crashed, there wasn't a "shutdown" entry in /usr/adm/wtmp at the time it was
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copied.
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.PP
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The above recipe is for a ordinary standard Minix installation with /usr on
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the second and last partition.
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.\" Minix-vmd usually has /usr on the third and
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.\" last partition (dosd3 / dosd8), its
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.\" .B mkfs
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.\" command requires a
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.\" .B "-t\ 2f"
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.\" option to specify the file system type as "V2 flex", and it knows if
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.\" it has crashed or not.
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.SS Backups
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In the recipe above you saw how simple it is to create a new system, just
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copy a disk file. It is equally simple to make a backup, you just copy the
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disk file. To make a test system: copy the disk file. To make another test
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system: copy the disk file. Let friends have their own Minix: copy the disk
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file again. (Exciting, eh?)
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.PP
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You may want to save a Minix disk file in a ZIP file to save space. It may
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look as a good idea to first run
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.B "make clean"
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in
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.B /usr/src
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to remove all the binary junk, but alas that has no effect at all.
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The disk file is compressed under DOS, and there it is unknown which blocks
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are in use and which are free. With the following trick you can make those
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deleted blocks compress really well:
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.PP
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.RS
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.nf
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cd /usr/tmp
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echo >junk
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while cat junk >>junk; do :; done
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sync
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rm junk
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.fi
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.RE
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.PP
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After these commands all free blocks contain newlines. Long runs of the
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same byte happen to compress by a factor 1000, so the unused disk blocks
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will almost disappear in the ZIP file.
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.\" Under Minix-vmd you can use
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.\" .PP
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.\" .RS
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.\" cp /dev/zero junk
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.\" .RE
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.\" .PP
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.\" instead of the echo/while pair of lines above. Standard Minix doesn't have
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.\" /dev/zero.
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.SS "FAT driver"
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The dos disk driver, described in
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.BR dosd (4),
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has two identities. By default you get the "\fBfile\fP" driver, that uses
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DOS file I/O calls to access a large DOS file as a disk. The other
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alternative is the "\fBFAT\fP" driver. The FAT driver sits on top of an
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ordinary Minix disk driver, and interprets a partition as a FAT (File Access
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Table) file system to find a file to use as a Minix disk. The result
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has the same effect as the file driver, except that no costly calls to DOS
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are made. To enable this feature you have to use the following Boot
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environment settings:
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.PP
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.RS
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.nf
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dosd = fat
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dosd0 = hd1:\eminix\edisk0.mnx
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.fi
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.RE
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.PP
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The
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.B dosd
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setting tells Minix to use the FAT driver, and the
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.B dosd0
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setting tells the Minix device and DOS file name to use. Disk I/O should
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be sped up nicely by this change, although typical use of Minix doesn't
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require fast disk I/O, so the difference won't be too noticable.
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.PP
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Support for FAT-32 (big file system support added in the later Windows 95
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releases) has not been tested very well. The FAT-12 and FAT-16 code has
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been used a lot, and seems safe. Note the risks inherent in these
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drivers: The file driver uses simple DOS file I/O calls, leaving it to
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DOS to know its own file system. The FAT driver interprets FAT file system
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structures by itself. Minix booted from a real hard disk partition can
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only use DOS disk files through the FAT driver.
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.SH "SEE ALSO"
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.BR dosd (4),
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.BR monitor (8),
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.BR usage (8).
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.SH NOTES
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Use at your own risk.
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.SH BUGS
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Hasn't been tried under Windows 98 yet.
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.PP
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Pray the deity of your choice will forgive you for running a UNIX-like
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system as an ordinary DOS program. The author of this code is already
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doomed. When his time comes the daemons wi*(&%*$%*&
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.br
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Memory fault \- core dumped
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.SH AUTHOR
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Kees J. Bot (kjb@cs.vu.nl)
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