923 lines
24 KiB
Plaintext
923 lines
24 KiB
Plaintext
UMSDOS HOW-TO
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Jacques Gelinas, jacques@solucorp.qc.ca
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v1.2, 2001-12-01
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Umsdos is a linux file system. It provide an alternative to the EXT2
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file-system. Its main goal is to achieve easier coexistence with Ms-
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DOS data by sharing the same partition. This document explain first
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how to use Umsdos in different configuration, and later explain its
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operation and try to provide some information letting you decide if it
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is a good choice for you (see UMSDOS-WHY-TO at the end).
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______________________________________________________________________
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Table of Contents
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1. Copyright and License
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2. UMSDOS: Where is it ?
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2.1 Copyright and License
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2.2 History
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2.3 Availability
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2.4 Distribution supporting it
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2.5 Home site
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2.6 Technical documentation
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2.7 Who wrote it
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3. Umsdos as your root partition
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3.1 The pseudo-root concept.
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3.2 Things to know about the pseudo-root
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4. Different topics about the operation of
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4.1 Mount option
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4.2 How to set defaults for the root
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4.3 To swap or not to swap
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5. How to boot a Umsdos system
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5.1 Loadlin
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5.2 From a floppy
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5.3 LILO
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5.4 How to defragment a
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5.5 Advance tricks
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6. Basic principle
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6.1 Introduction
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6.2 (EM
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6.3 Directory promotion
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6.4 How to promote:
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6.5 Using
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6.6 How to UN-promote
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6.7 What about files created during a
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7. Installation/UN-installation and some tricks
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7.1 The pseudo-root
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7.2 Preparing
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7.3 Making sure
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7.4 Oops releasing pseudo root ...
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7.5 How to UN-install a
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7.6 Moving a
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7.7 About installing 50
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8. Setting a
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9. UMSDOS-WHY-TO
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9.1 The goal of
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9.2 Who needs it
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9.3 Performance issue
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______________________________________________________________________
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1. Copyright and License
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This document is Copyright (c) 1995 by Jacques Gelinas.
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It is released under the terms of the GNU Free Documentation License.
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A copy of the license should have been distributed with it, or you can
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see a copy at http://www.fsf.org/licenses/fdl.html.
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2. UMSDOS: Where is it ?
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2.1. Copyright and License
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This document is Copyright (c) 1995, Jacques Gelinas.
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It may be distributed under the GNU Free Documentation License. You
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should have received a copy with it. If not, you can view it at
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http://www.fsf.org/licenses/fdl.html.
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2.2. History
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The Umsdos project was started in 1992 and made available to the net
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in January 1994 as a patch. It was included in the standard kernel
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distribution in July, starting with kernel 1.1.36.
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Umsdos was early adopted in the Slackware distribution even before it
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was officially included in the official kernel.
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Umsdos was improved starting at kernel 1.1.60. Its performance has
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been dramatically enhanced, especially for writing. Since 1.1.70
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(around this), it is stable again.
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A major bug was solve in Linux 1.2.2. This bug was causing some grief
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to users since the beginning (some file were silently renamed, giving
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the sad impression that they were deleted). Beware that Slackware 2.2
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is still shipping release 1.2.1 of the kernel, so has this bug.
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2.3. Availability
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It is available as a patch for kernel 1.0.x. It is built-in for kernel
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1.2. It can be compiled in or load as a module. Beware that for now,
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if you intend to load umsdos as a module, you must also use the Ms-DOS
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fs as a module. This come from a limitation in the module system (some
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symbols are only export when the drivers is installed as a module).
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2.4. Distribution supporting it
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So far, I think only Slackware does support it. I am surely wrong, so
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please send me info to correct this.
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2.5. Home site
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The home site for Umsdos is sunsite.unc.edu. Look in the directory
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/pub/Linux/system/Filesystems/umsdos.
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2.6. Technical documentation
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There is quite a lot of documentation about the internal of Umsdos. It
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is available both in HTML and text format at the same location as the
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utilities.
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As far as I know, the HTML version is not available online on any web
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site. You must down-load it and "UN-tar" it and read it locally.
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2.7. Who wrote it
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Jacques Gelinas jacques@solucorp.qc.ca
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3. Umsdos as your root partition
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3.1. The pseudo-root concept.
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With Umsdos, Linux can be installed in a standard DOS partition. Linux
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is then installed as a second (or third) OS in the partition. To avoid
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name collision (there is maybe a bin or tmp directory in the drive C:
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already), Umsdos use a smart trick: The pseudo-root.
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All Linux files are installed in a DOS subdirectory called linux,
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generally C: LINUX. The normal Linux/Unix directory structure goes
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there. So you get
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<20>
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C:\LINUX\BIN
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<20>
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C:\LINUX\ETC
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<20>
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C:\LINUX\LIB
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<20>
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C:\LINUX\ROOT
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<20>
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C:\LINUX\SBIN
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<20>
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C:\LINUX\TMP
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<20>
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C:\LINUX\USR
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<20>
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C:\LINUX\VAR
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When the Umsdos boot, it probes for the directory linux and then
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/linux/etc. If it exist, it activates the pseudo-root mode.
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Mostly, the pseudo-root mode switch the root of the partition to
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C:\\LINUX giving the conventional Unix directory layout
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<20>
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/bin
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<20>
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/etc
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<20>
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/lib
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<20>
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/root
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<20>
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/sbin
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<20>
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/tmp
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<20>
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/usr
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<20>
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/var
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To this list, it adds a new one called DOS. This one is a virtual
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directory.
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3.2. Things to know about the pseudo-root
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<20> This mode can only be triggered at boot time. There is no way to
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activate this by a mount command.
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<20> This mechanism is purely a different view of a normal Umsdos file-
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system. This means that a partition normally used as a root
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partition can be normally mounted. There won't be any pseudo-root
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effect.
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For example, if you boot linux with a maintenance floppy and mount
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your normal root partition in /mnt, you will find all your linux
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directory in /mnt/linux/bin, /mnt/linux/etc and so on.
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4. Different topics about the operation of Umsdos
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4.1. Mount option
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You can use the same mount option as for the Ms-DOS file system. The
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option conv= is questionable on a Umsdos system. I suggest to avoid
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it. Mostly the option you may want to look at are
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<20> uid=
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<20> gid=
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<20> umask=
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Just remember that Umsdos manage non promoted directory the same way
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as the Ms-DOS file system. The option above will apply globally to all
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non promoted directory. uid setup the default owner, gid setup the
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default group and umask setup the default permissions.
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4.2. How to set defaults for the root
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umssetup was created to provide at run time default ownership for the
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root partition. For other Umsdos partition, mount option may be used
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or umssetup. Storing mount option in /etc/fstab is the prefered way
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for non root partition. Here is an example. Put this in
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/etc/rc.d/rc.S.
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/sbin/umssetup -u jack -g group -m 0755 /
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4.3. To swap or not to swap
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Using a swap file is generally slower than a swap partition. It is
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however much more flexible. You can setup a swap file in a Umsdos
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partition the same way you do it for any other Linux file systems. For
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example, to setup a 8 megabytes swap file in the root directory:
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dd if=/dev/zero bs=1024k count=8 of=/swap
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mkswap /swap 8192
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sync
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swapon /swap
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Once done, you can put the following line in /etc/fstab
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/swap swap swap default
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And the swap file will be activated at each boot (There is generally a
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"swapon -a" in /etc/rc.d/rc.S).
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5. How to boot a Umsdos system
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5.1. Loadlin
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The package lodlin15.tgz available from sunsite.unc.edu in
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/pub/Linux/system/Bootutils. This utility is particularly suited to
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boot a Umsdos system. Generally all you need to do is
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Boot DOS
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C:>loadlinx zimage root=D:
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where zimage is a normal kernel image (compressed) simply copied
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somewhere in the DOS drive. D: is the DOS drive where you have
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installed Linux.
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5.2. From a floppy
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Booting a Umsdos system from a floppy is not different from booting a
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Ext2 system. You need a kernel zImage file properly initialize to
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locate your root Umsdos partition. This is generally achieved using
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the command rdev. The following sequence will initialize a zImage and
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put it on a floppy.
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rdev zImage /dev/hda1
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rdev -R zImage 0
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dd if=zImage bs=8192 of=/dev/fd0
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If this looks confusing, just format a boot-able DOS floppy and put
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the following component on it.
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<20> loadlin.exe
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<20> loadlinx.exe
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<20> zimage
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and setup the autoexec.bat like this
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loadlinx zimage rw root=C:
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5.3. LILO
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LILO, the official Linux boot loader can also be used to boot a Umsdos
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system. I have no experience with it though. Since 1.1.60, it should
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work. Please email if you know something.
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5.4. How to defragment a Umsdos partition
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It can be done using any popular DOS tool. There is nothing particular
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about file produced by Umsdos. And Umsdos do not expect anything
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particular (directory layout, directory entry sequence, etc...) from
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the file system under it.
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As far as I know, there is no Linux tool to achieve this.
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5.5. Advance tricks
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Umsdos rely on the --linux-.--- which rely on the DOS directory. Some
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users may want to experiment a bit. The utility udosctl part of the
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umsdos_progs package (containing umssync and umssetup) allows basic
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directory operation (listing, deletion) independently on the
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--linux-.--- and the DOS directory.
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6. Basic principle
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6.1. Introduction
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Umsdos map Linux files directly to Ms-DOS files. This is a one for
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one translation. File content is not manipulated at all. Umsdos only
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works on names. For special files (links and devices for example), it
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introduces special management.
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For each directory, there is a file named --linux-.---.
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6.2. Umsdos can replace the Ms-DOS file-system.
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Umsdos can be thought as a general purpose superset of the Ms-DOS file
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system of linux. In fact this capability or flexibility yields much
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confusion about Umsdos. Here is why. Try to mount a newly formatted
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DOS floppy like this.
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mount -t umsdos /dev/fd0 /mnt
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And do this,
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ls / >/mnt/LONGFILENAME
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ls -l /mnt
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You will get the following result
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-rwxr-xr-x 1 root root 302 Apr 14 23:25 longfile
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So far, it seems that the Umsdos file system does not do much more (in
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fact nothing at all) than the normal Ms-DOS file system of Linux.
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???
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6.3. Directory promotion
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Pretty unimpressive so far. Here is the trick. Unless promoted a DOS
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directory will be managed the same way with Umsdos than the Ms-DOS
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file-system will. Umsdos use a special file in each subdirectory to
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achieve the translation between the extended capabilities (long name,
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ownership, etc...) of Umsdos and the limitation of the DOS file-
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system. This file is invisible to Umsdos users, but visible when you
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boot DOS. To avoid cluttering the DOS partition with those file
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(--linux-.---) uselessly, the file is now optional. If absent, Umsdos
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behave like Ms-DOS.
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When a directory is promoted, any subsequent operation will be done
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with the full semantic normally available to Unix and Linux users. And
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all subdirectory created afterward will be silently promoted.
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This feature allows you to logically organize your DOS partition into
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DOS stuff and Linux stuff. It is important to understand that those
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--linux-.--- file do take some place (generally 2k per directory). DOS
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generally use large cluster (as big as 16k for a 500meg partition), so
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avoiding putting --linux-.--- everywhere can save your day.
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6.4. How to promote: /sbin/umssync
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A directory can be promoted any time using /sbin/umssync. It can be
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used at any time. Promoting a directory do the following operation
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<20> Create a --linux-.---.
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<20> Establish a one to one relation between the --linux-.--- and the
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current content of the directory.
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/sbin/umssync maintain an existing --linux-.--- file. It does not
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create it from scratch all the time. It simply add missing entries in
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it (Files created during a DOS session). It will also removed files
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which do not exist anymore in the DOS directory from the --linux-.---.
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umssync gets its name from that. It put --linux-.--- in sync with the
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underlying DOS directory.
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6.5. Using /sbin/umssync at boot time
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It is a good idea to place a call to /sbin/umssync at the end of your
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/etc/rc.d/rc.S if it's not there. The following command is adequate
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for most system:
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/sbin/umssync -r99 -c -i+ /
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The -c option prevent umssync from promoting directories. It will only
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update existing --linux-.---.
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This command is useful if you access Linux directory during a DOS
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session. Linux has no efficient way to tell that a directory has been
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modified by DOS so Umsdos can't do a umssync operation as needed.
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6.6. How to UN-promote
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Remove the --linux-.--- file using DOS. You will be sorry.
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6.7. What about files created during a DOS session ?
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Unless you use umssync on a directory where files have been added or
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removed by DOS, you will notice some problems:
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<20> It won't crash the system nor it won't cause major problems, only
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annoyance :-)
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<20> Files created by DOS.
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<20> They will be invisible in Linux.
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<20> When trying to create a file with the same name, you will get an
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error message stating that the file already exist.
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<20> This creates more confusion that real problem. It does not harm the
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file system.
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<20> Files deleted by DOS won't cause problem. Umsdos will notice the
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absence at the first access. A message will be output (and
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generally written into /var/adm/syslog).
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|
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7. Installation/UN-installation and some tricks
|
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|
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The installation of a Umsdos is not much different from the
|
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installation of an ordinary (Ext2 based) Linux system.
|
||
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There are two main differences.
|
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7.1. The pseudo-root /mnt/linux
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The normal steps for an installation are
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1. Setting a partition with fdisk and formatting it.
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2. Mounting it as /mnt relative to our installation root disk.
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3. Copy all packages into /mnt.
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With Umsdos, the step 1 is not required (wasn't it the goal of Umsdos
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not to reformat ?).
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It is possible to install a Umsdos system just by copying all packages
|
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into /mnt. This will certainly work. But it will create a bunch of
|
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subdirectories into your DOS root directory (C:) and you won't like
|
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it. This is the reason all Umsdos installation use the pseudo-root.
|
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And this is the major difference between a normal Ext2 installation
|
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and a Umsdos one: All files are copied into /mnt/linux.
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7.2. Preparing /mnt/linux
|
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/mnt/linux is not an ordinary directory. It has to be promoted so it
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will correctly handle Linux long file name and special files (links,
|
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device). The step required to setup /mnt/linux are:
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|
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1. mkdir /mnt/linux
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2. umssync /mnt/linux
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||
That's it!
|
||
|
||
|
||
7.3. Making sure /mnt/linux is correctly setup
|
||
|
||
Even if the setup of /mnt/linux is pretty simple, there are many
|
||
installation package out there who get it wrong. How can ?
|
||
|
||
The biggest installation problem come from an incompatible umssync
|
||
program. Umsdos has been update in linux 1.1.88 (Can't remember
|
||
exactly) and a flaw was uncovered in umssync. To avoid confusion in
|
||
the Linux community, it was decided to raise the compatibility level
|
||
required for all Umsdos tools. Old version of the tools were simply
|
||
rejected.
|
||
|
||
It sounds like many distribution did not update their umssync utility
|
||
on the installation disk.
|
||
|
||
There are still many distribution like this out there. The net result
|
||
is that the directory /mnt/linux is not promoted at all and will
|
||
truncate all long file name and will reject all special file.
|
||
|
||
It is possible to do a test very early during the installation to find
|
||
out if something went wrong. Thanks to the pseudo console mechanism of
|
||
Linux, you can do that without leaving the installation program. Do
|
||
the following steps:
|
||
|
||
|
||
1. Press Alt-F2 (Alt key at the same time as the F2 key).
|
||
|
||
2. login as root.
|
||
|
||
3. cd /mnt/linux
|
||
|
||
If this fail, you are trying this too early. A good time to do this
|
||
is at the end of the packages selection.
|
||
|
||
4. >TOTO
|
||
|
||
5. ls -l
|
||
|
||
You should see an empty file TOTO in uppercase. If you see it in
|
||
lowercase, something went wrong. Try to do the umssync step again.
|
||
umssync can be use over and over without problem.
|
||
|
||
umssync .
|
||
|
||
If there is no error message, try the TOTO test again. If TOTO
|
||
appears fine, then all is OK. Something is strange in this
|
||
installation, but you just save it. Continue
|
||
|
||
|
||
6. Press Alt-F1 to get back to the installation screen.
|
||
|
||
If the test fail, the best fix is to get a newer installation root
|
||
disk. You can generally fix this root disk by installing a newer
|
||
version of umssync. This is not difficult but required a working Linux
|
||
system. You simply have to mount the root disk floppy and replace the
|
||
offending umssync with a new one.
|
||
|
||
|
||
7.4. Oops releasing pseudo root ...
|
||
|
||
Most Umsdos installation which fail, do this by printing this strange
|
||
message. This is not a bug in Umsdos although the message looks
|
||
strange. Here are the known causes.
|
||
|
||
|
||
<20> The most common one
|
||
|
||
The Slackware installation try to setup a swap file very early
|
||
during the installation. To do so, it asks you to select a
|
||
partition (dos drive), then mount it and set the swap file.
|
||
|
||
When installing a Slackware system, you must setup the target
|
||
partition prior to install. This normally mounts the DOS partition
|
||
on /mnt, creates the /mnt/linux directory and applies umssync on
|
||
it.
|
||
|
||
This is where most problems come from. Most user just forget the
|
||
"setup target partition" step and go directly to the rest of the
|
||
installation. Since /mnt is already mounted, this mistake goes
|
||
unnotice. This means that /mnt/linux was not created properly (Not
|
||
promoted). All special files and links and long names can't be
|
||
created properly.
|
||
|
||
|
||
<20> Invalid umssync utility
|
||
|
||
/mnt/linux was improperly setup-ed. Generally caused by an improper
|
||
umssync utility on the installation root disk.
|
||
|
||
<20> Old bug in umsdos
|
||
|
||
There was a bug in Umsdos prior to Linux 1.2.2. The pseudo-root
|
||
mode would not activate properly if the file /etc/init was missing.
|
||
init is now located in /sbin. You can fix it by getting a newer
|
||
kernel. This is recommended because another bug was uncover and
|
||
fixed in 1.2.2.
|
||
|
||
If you can't upgrade, do this
|
||
|
||
|
||
1. Boot from you installation disk.
|
||
|
||
2. Login as root.
|
||
|
||
3. mount -t umsdos /dev/hdXX /mnt
|
||
|
||
where /dev/hdXX is your DOS partition.
|
||
|
||
4. cd /mnt/linux/etc
|
||
|
||
5. ln -s ../sbin/init init
|
||
|
||
6. cd /
|
||
|
||
7. Ctrl-Alt-Del
|
||
|
||
8. Boot your Umsdos normally.
|
||
|
||
Unfortunatly, the first two (Installation problems) produce a
|
||
completly unusable installation. Uninstall it (See next section) and
|
||
install again.
|
||
|
||
|
||
|
||
7.5. How to UN-install a Umsdos system
|
||
|
||
One neat thing about Umsdos and its pseudo-root mechanism, is that you
|
||
can UN-install it without pain. You just boot DOS and recursively
|
||
delete the linux directory. That's all. Umsdos requires no special
|
||
drivers in the config.sys, nor it creates anything special outside of
|
||
the linux directory.
|
||
|
||
|
||
7.6. Moving a Umsdos system to another DOS drive
|
||
|
||
This can be done from Linux or from DOS. You just have to copy
|
||
recursively the linux directory from one drive to the other. After
|
||
that you will have to adjust you boot mechanism (generally loadlin
|
||
command) and the /etc/fstab file.
|
||
Umsdos can live on any DOS drive. There is no need to install it on
|
||
the C: drive, nor it is important to have it on the first hard drive.
|
||
It does not matter at all.
|
||
|
||
In fact, one may decide to have several Umsdos installations on
|
||
different drive just to do experiments.
|
||
|
||
|
||
7.7. About installing 50 Umsdos systems.
|
||
|
||
How about installing a bunch of Linux systems in no time ?
|
||
|
||
Umsdos systems are living in a DOS world. You can take advantage of
|
||
this if you wish to install Linux easily.
|
||
|
||
You can install and configure a Umsdos system at your site. When you
|
||
are satisfied with the configuration and the different packages you
|
||
have selected, you can boot DOS and copy the complete linux directory
|
||
to your DOS file server. Then you go to other DOS station and simply
|
||
copy the files on the network drive to the local drive. That's it.
|
||
Only adjust the boot script (Loadlinx) and go.
|
||
|
||
With minimal adjustment (Host name, IP number), anyone will be able to
|
||
install a Linux system in a matter of minute.
|
||
|
||
Interest readers may note that installing Linux systems by copying
|
||
running system also works for any other Linux systems, including Ext2
|
||
based one.
|
||
|
||
One beauty of Linux is that there is no hidden files which have to be
|
||
install by magic installation program.
|
||
|
||
|
||
8. Setting a Linux section in a DOS partition
|
||
|
||
Umsdos has some use even for Ext2 (Native Linux file-system) users.
|
||
One common scenario is this:
|
||
|
||
|
||
<20> Linux being your OS of choice, the Linux partition start to fill
|
||
and fill and fill.
|
||
|
||
<20> Your DOS partition is collecting dust, being half empty.
|
||
|
||
<20> You are suddenly out of space in the Ext2 partition.
|
||
|
||
<20> You are still not sure you want to get rid of DOS.
|
||
|
||
Umsdos may save the day here. You can setup a Linux directory in the
|
||
DOS partition and use it without restriction for Linux usage. For
|
||
example, say you want to setup a new directory named "extra" in your
|
||
C: drive. And you want this directory to behave as a normal Linux
|
||
directory. Do this (assuming that C: is /dev/hda1).
|
||
|
||
|
||
|
||
mkdir /c
|
||
/sbin/mount -t umsdos /dev/hda1 /c
|
||
mkdir /c/extra
|
||
umssync /c/extra
|
||
|
||
|
||
|
||
You must be root to do this.
|
||
|
||
By setting up /etc/fstab like this, you will always have access to the
|
||
/c/extra directory.
|
||
|
||
|
||
|
||
9. UMSDOS-WHY-TO
|
||
|
||
Explaining how to operate or install a Umsdos system is not enough.
|
||
Most people are seeking some advises about using Umsdos or not.
|
||
|
||
|
||
|
||
9.1. The goal of Umsdos
|
||
|
||
The goal of Umsdos was to ease the installation of Linux. An other
|
||
goal was to ease its UN-installation. The idea here was to promote
|
||
the spreading of Linux. Installing a new OS on a system is always
|
||
troublesome. OS/2 for one will happily pollute your C: root with a
|
||
bunch of new directories. If you are clever like me, it will also
|
||
erase your config.sys and autoexec.bat files :-(
|
||
|
||
The pseudo-root feature of Umsdos avoid this unwanted invasion. Linux
|
||
can be UN-install without side effect.
|
||
|
||
|
||
9.2. Who needs it
|
||
|
||
If you have a small hard drive, Umsdos will allow you to share disk
|
||
space between DOS and Linux. A disk below 300 megs is in my opinion a
|
||
small disk. This opinion is based on the size of the different package
|
||
available today. One popular word processor may eat as much as 70
|
||
megabytes if you select all features.
|
||
|
||
If you have a larger drive, you may consider having a dedicated Linux
|
||
partition running the Ext2 file-system. Ext2 use a smaller cluster
|
||
size that DOS (1k in fact) so installing many small files will eat
|
||
less space than in a Umsdos partition.
|
||
|
||
|
||
9.3. Performance issue
|
||
|
||
The following point apply to Umsdos compared with Ext2.
|
||
|
||
|
||
<20> Directory management is faster on Ext2. This come from the overhead
|
||
of the double directory structure of Umsdos.
|
||
|
||
<20> File access (reading and writing) is probably faster on Umsdos than
|
||
Ext2. This come from the simplicity of the FAT file-system used by
|
||
DOS.
|
||
|
||
Beware that this simplicity come with a cost:
|
||
|
||
|
||
<20> A maximum of around 65,000 files or clusters per partitions. This
|
||
also means that a 500 megabytes partition will use cluster 16k
|
||
large. In other word, a file containing a single byte will use 16k
|
||
of disk storage.
|
||
|
||
<20> Everything is controlled by the FAT located at the beginning of the
|
||
hard drive. The DOS file-system is probably more fragile because of
|
||
this.
|
||
|
||
|
||
<20> No provision to avoid fragmentation of files. A Umsdos system will
|
||
generally be used as a single user workstation. In this case, this
|
||
does not matter much. As a multi-user engine, files will get
|
||
spread-ed all around the drive, lowering file access performance.
|
||
|
||
<20> Symbolic links are stored in normal file. If you intend to have a
|
||
lot of them, you will find that Umsdos use quite a lot of disk
|
||
space compared to Ext2.
|
||
|
||
|
||
|