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Linux Swap Space Mini-HOWTO
Rahul Sundaram rahulsundaram@yahoo.co.in <mailto:rahulsun­ daram AT yahoo DOT co DOT in>
v1.6, 2002-12-27

This Linux Mini-HOWTO describes how to share your Linux swap partition with Windows.


Table of Contents

  1. Introduction
  2. What you need
  3. Recent Changes and versions
  4. Administrative

    4.1 Copyright 4.2 Disclaimer

  5. Before you begin
  6. The Procedure

    6.1 Turn off swapping and create a DOS partition 6.2 Tell Windows the location of the new swap file

    6.2.1 (BF 6.2.2 (BF 6.3 Back up the Total Special Sectors 6.4 Modify the initialization and shutdown scripts to handle our new configuration 6.5 Reenable swapping

  7. A couple of notes
  8. What are we exactly doing ?
  9. The swapinit.sh script
  10. The swaphalt.sh script
  11. The msinfo.sh script
  12. The original msinfo file
  13. Acknowledgements, feedback and dedication

  1. Introduction

Many people use both Linux and MS-Windows. The ability to do so is an important part of "the Linux revolution"; i.e. letting people experiment with (and get hooked on) Linux while still being able to run their off-the-shelf software. Since both Linux and MS-Windows use virtual memory with swap to disk, a frequently occurring question in comp.os.linux.setup is how to share swap spaces, in order to reduce the amount of disk space needed.

There are several methods for sharing swap spaces, the one described in this document is probably the most complicated one but is the only one I have encountered that allows maximum performance for both environments without the risk of trashing a disk partition. If you are using DOS, then many DOS applications manage their own swap files. You can also share the Linux swap partition with these applications.

2. What you need

This procedure have a few requirements that need to be filled. I strongly recommend that you fill these requirements anyway, as there are several problems with older versions.

  1. MS-DOS 5.0 or newer and MS-Windows 3.1/3.11 OR MS-Windows 95/98
  2. A shutdown/init that knows to run a file on shutdown. (The SysVinit-2.50 package can do this, for example. SysVinit-2.50 is available from sunsite.unc.edu in /pub/Linux/system/Daemons. Almost all current distributions use this init package.)
  3. Recent Changes and versions
    • Version 1.3 -- Written by H. Peter Anvin, and was not maintained from 15 Jan 1998.
    • Version 1.4 -- Based on v1.3, but added more details.Rahul U. Joshi started maintainance
    • Version 1.42 -- Deleted the recovery section for v1.4 users an v1.4 never actually appeared on the LDP website.
    • Version 1.5 -- Rahul U.Joshi stopped maintainance on 18 January 2000.Currently being maintained by Rahul Sundaram.
    • Version 1.6 -- Renamed from Linux Swap space to this one.

Modifications by Rahul U. Joshi

Date: 26 Nov 1999

  • Added Windows 95/98 specific details.
  • Added Red Hat Linux specific details.
  • Modified the msinfo program.
  • Added sections 5 to 12.
  • Completely revamped the "Procedure" section to make it more understandable.
  • Split up the swap initialization and halt into two shell scripts.
  • Modified the scripts to handle signature verification more than once.
  • Added details about new type swap areas.
  • Added more reliable schemes. 4. Administrative

4.1. Copyright

This mini-HOWTO is Copyright Rahul Sundaram.All rights reserved.This document is licensed under the Linux Documentation Project license <http://tldp.org/copyright.html>.I welcome any kind of commercial distrubution but I would like to receive information regarding this.I would also help anyone willing to translate this document.If you require any exceptions to the licensing terms please contact me Rahul Sundaram <mailto:rahulsundaram AT yahoo DOT co DOT in>. The latest version of this document is always available at the Linux Documentation website at <http://tldp.org/HOWTO/mini/Automount.html>.

4.2. Disclaimer

Although I have tried my best to bring out various facts, the author is not responsible for any damage due to the actions taken based upon the information contained in this document. It is impossible to test the things under all the configurations, so probably some of the hints given in this document may be buggy and may not work on your system. In case you trace the bug, let me know it first !

This document is provided ``as is''. I put great effort into writing it as accurately as I could, but you use the information contained in it at your own risk. In no event shall I be liable for any damages resulting from the use of this work.

In case you are planning to include this HOWTO on some distribution medium or in print, I will like to have an acknowledgement e-mail (just for my record). In that case, I may also be able to send you the latest version of the document.

5. Before you begin

This is not a step by step HOWTO. The reader is expected to first read the entire document so that he (or she) becomes aware of the possible pitfalls and performance bottlenecks. After having a fair idea as to what steps are to be taken, he (or she) can then follow the next section in a step by step manner. Since you will be playing as a root and that too with the system initialization files, be alert as to what you are doing. Write in those files comments for those sections that you added, and when you want to remove a section, do not delete it. Instead just comment it out. (In shell scripts comments begin with a pound(#) sign). In case things go wrong, you may restore your original configuration by removing the changes you did. Although you are not required to know shell scripting since I have given all those that would be needed, some knowledge may be advantageous both for understanding as well for debugging.

6. The Procedure

NOTE: This procedure has been written keeping in mind RedHat Linux 6.0 Although this procedure in general is applicable for all Linux distributions, the details may vary. You are welcome to add the details for your distribution. Many users will already have a swap partition devoted to Linux. I assume you have one.

6.1. Turn off swapping and create a DOS partition

·

     Boot Linux. Turn off swapping by editing the /etc/fstab file and
     commenting the line that describes your swap partition.

·

     Using fdisk under Linux, delete the swap partition in order to
     create free space on the disk.

·

     Boot DOS.  Create a DOS partition (using FDISK) the size = the size
     swap space you want. If you cannot create the partition (probably
     because DOS FDISK says that all the space in extended partition is
     allocated to the logical drive), you can use fdisk or cfdisk under
     Linux to create the partition. You can even just change the type of
     your swap partition from 82h (Linux Swap) to 06h (FAT16).  In that
     case you don't need to delete the swap partition, just change the
     type.

·

     Once you have created the partition, Boot DOS if you are not
     already in DOS.  DOS will be assigned a drive letter to your new
     partition. Use that drive letter instead of X whenever these
     instructions lists a command like "LABEL X:" or "COPY FOO
     X:DUMMY.DAT"

·

Format this partition using the DOS FORMAT command.

C:\>FORMAT X:

·

     Set the volume label on this partition to "SWAP SPACE" using the
     DOS LABEL command.  Verify it by the DIR command.  Please do this
     as a separate step.  Some versions of FORMAT do not seem to put the
     volume label in the boot sector as it should.  [Note: some people
     has written me saying the volume label is stored in the root
     directory.  Yes, but at least since DOS 5.0 it has also been in the
     boot sector.]

       C:\>LABEL X:
       C:\>DIR X:

·

At this stage, you have a DOS partition ready for use for swapping.

6.2. Tell Windows the location of the new swap file

6.2.1. For Windows 3.1 users

·

     Start Windows.  Go to the Control Panel, select "386 Enhanced".
     Select "Virtual Memory" and create a Windows Permanent swap file on
     drive X: of maximum size (Windows will tell you the maximum size).
     Windows may complain saying it will not use a swap file that big.
     Ignore the message and create the file anyway.

·

Exit Windows.

6.2.2. For Windows 95/98 users

·

     Start Windows. Go to the Control Panel (Start | Settings | Control
     panel).  Double click the System icon. In the resulting System
     Properties dialog box, select the Performance tab. Now click the
     Virtual Memory button. This will bring up the Virtual Memory dialog
     box. Select "Let me specify my own virtual memory settings". Select
     the drive you intend to share as swap space with Linux (X:). Keep
     the Maximum and Minimum values as selected by Windows. Click OK.
     Windows will prompt you to restart your computer. Do it.

·

     When you restart Windows, you will see that the win386.swp file has
     been created on the X: drive. In addition, there is also the
     Recycled folder.  Since you don't intend to store any other files
     on this drive and also a single file on this partition will be
     convienent, tell Windows not to maintain Recycle Bin for this (X:)
     drive. On the Desktop, left click the Recycle Bin icon, and in the
     resulting pop-up menu, click Properties. This will bring up the
     Recycle Bin Properties dialog box. Click the Global tab and select
     "Configure drives independently". Now click the tab for X: drive
     (which will have the label SWAP SPACE). In this dialog box, move
     the slider for "Maximum size of Recycle Bin" to 0 percent. The
     "Space Reserved" entry should now read as 0 bytes. Click OK.
     Restart your computer.

·

     Now that you are not maintaining the Recycle Bin for drive X:,
     ideally the RECYCLED folder from X: must be deleted by Windows. Not
     only Windows doesn't does that, but also does not allow you to
     delete the folder. But as I said earlier, this folder is now
     unnecessary and we want drive X: to contain only the win386.swp
     file. For that purpose, first start your computer in MS-DOS mode.
     Select Start | Shut Down | Restart your computer in MS-DOS mode, or
     if you are booting Windows, press F8 at the start, and then from
     the startup menu, select Command Prompt only.  Once you are in MS-
     DOS mode, type the following commands:

       C:\>X:
       X:\>ATTRIB -R -H -S RECYCLED
       X:\>DELTREE RECYCLED

Now you have drive X: containing only win386.swp. You can verify this using the various options for the dircommand. This does not mean that the RECYCLED folder will not be there on drive X:. When Windows boots up and finds that there is no RECYCLED folder on X:, it will create it automatically. However, when we will be restoring X: from Linux, it will simply contain win386.swp file. If anyone is aware of a method to prevent Windows from creating the RECYCLED folder, please e-mail me.

·

Disk Cleanup troubles you ?

     If you have Disk Cleanup installed, then ocassionally Windows comes
     out with a "Low disk space on drive X:". Since we are using the
     entire X: drive for swapping, there is no need to have any free
     space on X:. To prevent this dialog box from appearing, start Disk
     Cleanup (point to Start | Programs | Accessories | System Tools |
     Disk Cleanup). In the resulting dialog box, select the X: drive and
     click OK. The "Disk Cleanup for drive X:" dialog box appears. Click
     the "Settings" tab and uncheck the "If this drive runs low on disk
     ... blah blah blah" check box.

>From this stage onwards, Windows will assume that it's swap file is on drive X:. So the drive X: must be intact each time you boot Windows. If you are using some additional system utilities like Norton Utilities for Windows 95, then you should probably consult the online help or the manuals to keep them informed of the changes in the settings, otherwise they may come out with an error message.

6.3. Back up the Total Special Sectors

·

Boot Linux, then log in as root.

·

     Use the fdisk command to find the name of the partition and its
     size in blocks.  Create a symbolic link from /dev/winswap to this
     partition.  If the partition is hda7, then type:

       # ln -s /dev/hda7 /dev/winswap

[NOTE TO PURISTS: Please use a symlink. The name of this partition is going to go into several configuration files and inconsistencies could be fatal.]

·

     Find the "Total Special Sectors" for the swap drive. These are
     nothing but the total number of sectors required for the boot
     sector, FAT and root directory.  There are a number of ways to find
     this number. Simplest copy the ``msinfo.sh'' file using your
     favourite editor. Give the following commands at the  shell prompt

       # cp Swap-Space-HOWTO msinfo.sh
       # chmod +x msinfo.sh

(Much easier if you use one of the editors with KDE or GNOME)

Now, open the msinfo.sh file in the editor and delete everything except the msinfo.sh file in section 8. Now run this file as

# ./msinfo.sh /dev/winswap

The program will print the some information about the swap partition. Take note at the number saying "Total special sectors", and verify that the volume label says "SWAP SPACE". If it does not, reboot DOS and re-do the LABEL command.

·

     Note: You can also find the "Total Special Sectors" using tools
     that can display the Boot sector like the Norton Disk Editor or
     minfo from mtools under Linux. For Norton Disk Editor, select
     "Boot Sector" from the Object menu. Note down the following entries
     :

Reserved Sectors at beginning : r

  FAT Copies                    : f
  Sectors per FAT               : s
  Root directory entries        : r

Now the "Total Special Sectors" is given by

T = r + (s * f) + (d / 16)

However, using the above program is more convienent.

Let us denote these Total Special Sectors by XXX.

·

     [Optional step] Windows may occasionally leave some space on the
     partition, even if it is told not to.  Don't attempt to use this
     space, since it will be erased any time you run Linux.  If you want
     to avoid accidentally using it (and lose data), you can create a
     dummy file that fills that space by using the following commands:

       mkdir /mnt
       mount -t msdos /dev/winswap /mnt
       dd if=/dev/zero of=/mnt/dummy.fil
       umount /mnt

The dd command will report "No space left on device". This is exactly what you want.

·

Type on the shell prompt:

       # dd if=/dev/winswap bs=512 count=XXX | gzip -9 > /etc/winswap.gz
                                         ^^^

... where XXX is replaced with the "Total special sectors" number.

Here we are saving the Total Special Sectors in a compressed form in the file /etc/winswap.gz

6.4. Modify the initialization and shutdown scripts to handle our new configuration

·

     Now, we will modify our initalization scripts so that swap space
     will be create on the partition each time Linux starts and the
     DOS/Windows special sectors will be restored each time Linux shut
     downs.

·

     Instead of placing the command for handling the details directly in
     the initialization scripts, we will prepare two separate files
     called swapinit.sh and swaphalt.sh. One sample of these files that
     should work under Red Hat Linux is given in section at the end. You
     can choose to place these files under any directory, preferably
     /etc/rc.d/init.d. Create the two files in this directory and copy
     into then the scripts given in sections at the end. One simple way
     is to copy this HOWTO in these files as,

       # cp Swap-Space-HOWTO  /etc/rc.d/init.d/swapinit.sh
       # cp Swap-Space-HOWTO  /etc/rc.d/init.d/swaphalt.sh

and then using your favourite editor, delete all execpt the required part. Now make these file "executable" by giving the following commands

       # chmod +x swapinit.sh
       # chmod +x swaphalt.sh

·

     Run fdisk and find the size of the swap partition in blocks. In
     both the above files (swap????.sh) replace the YYYYY by this
     number.

·

     Check the name of the shutdown file.  For SysVinit this is the file
     listed in the following line of /etc/inittab; add it if you don't
     have it.

# Runlevel 0 means shut down the system l0:0:wait:/etc/brc

(Under Red Hat Linux, this file probably will be /etc/rc.d/init.d/halt) If you are not in a position to find it out, browse through the /etc directory and find the initialization file that contains the "swapon -a" command. Only this much for now !

For the remainder of this file, I will assume the filename was /etc/rc.d/init.d/halt (halt for short).

·

     Check the name of your system initialization file. For SysVinit,
     this is the file listed in the following line of /etc/inittab.

       # System initialization
       si::sysinit:/etc/rc.d/rc.sysinit

In case of your distribution, your file may be different. I assume that the file is /etc/rc.d/rc.sysinit (rc.sysinit for short)

·

     Add the following piece of code to your initialization file
     (rc.sysinit), in place of the "swapon -a" command. You may consider
     not deleting but just commenting the original commands so that if
     something goes wrong, we can restore the script to it's initial
     state.

     If your swapon is in /etc, replace /sbin/swapon with /etc/swapon.
     If it is in /bin, replace with /bin/swapon.  Do the same for
     mkswap.

       # -----------------------------------------------------------------------
       # removed by yourname
       # Start up swapping.
       # action "Activating swap partitions" swapon -a
       # -----------------------------------------------------------------------

       # ----------------------------------------------------------------------
       # added by yourname
       # Verify and initialize swap space
       #
       /etc/rc.d/init.d/swapinit.sh
       # ----------------------------------------------------------------------

·

     A simple way to paste the text is to start two Virtual Consoles.
     Log as  a root in both cases. Use your favourite editor to open
     this HOWTO on one console and the script to be modified on other
     console. Now select the above code with your mouse and switch to
     the other console. Place the cursor at the desired position to
     paste and press the right mouse button. The selected text will be
     copied.

·

     Add the following piece of code to your shutdown file (halt).Put
     this after any command that might need swap to be in place.
     Normally, your halt file will have the "swapoff -a" command. First
     replace the -a by /dev/winswap. Then immediately after that
     section, add the following commands.

     Note for RedHat Linux 6.1 :  It seems that Red Hat Linux 6.1 halt
     script automatically finds all the swap partitions and turns of
     swapping.  So, RedHat Linux 6.1 users need not replace the swapoff
     $SWAPS comamnd by the swapoff -a command. In that case, just add
     the /etc/rc.d/init.d/swaphalt.sh command to the halt file

       # ------------------------------------------------------------------------
       # Modified by yourname
       # replaced "swapoff -a" by "swapoff /dev/winswap"
       #
       # Turn off swap, then unmount file systems.
       runcmd "Turning off swap and accounting" swapoff /dev/winswap
       [ -x /sbin/accton ] && /sbin/accton
       # ------------------------------------------------------------------------

       # ------------------------------------------------------------------------
       # Added by yourname
       # check swap signature and restore Windows swap info
       /etc/rc.d/init.d/swaphalt.sh
       # ------------------------------------------------------------------------

6.5. Reenable swapping

Uncomment the line in /etc/fstab that you commented earlier. (Not really necessary, since we now do not refer to fstab for swap partitions). Reboot Linux. You should now have swapping on the new swap device.

7. A couple of notes

·

     There is no need to add /dev/winswap to your /etc/fstab file.  In
     fact, it is probably wise not to do so (except possibly as a
     comment).

·

     If your Linux session crashes or otherwise exits without running
     /etc/rc.d/init.d/halt, you will need to reboot and exit Linux
     before swapping in Windows will work.  It is also possible to
     FORMAT X: and re-create the Windows swap file.  The only way around
     this would be to put the equivalent of the /.../halt commands in
     the DOS AUTOEXEC.BAT file. I have tried to write some programs to
     do this, but that turned out to be a hell lot of trouble !  First
     and foremost, simply restoring the total special sectors doesn't
     please DOS. Along with that, it seems you need to modify some
     internal data structures so that DOS starts recognizing your drive,
     otherwise DOS comes out with the error message:

       Invalid media type reading drive X:
       Abort, Retry or Fail ?

Since I am not aware of many details of DOS's or Windows's handling of disk drives, I think at this point, you may consult some DOS expert. Of course, if you are not concerned about the booting time, then you can simply add the command to perform an unconditional FORMAT of X: and then restore the TSS's. May be there are some other solutions. If you are aware of one, please e-mail me today !

·

     One way to restore your Windows swap partition is to start Linux,
     disable swapping as described above, and then use the following
     command :

       # swapoff -a
       # zcat /etc/winswap.gz > /dev/winswap
       # reboot

·

     Why to delete the RECYCLED folder ?  According to the procedure
     mentioned above, you must delete the RECYCLED folder. This is
     necessary because we will be saving and restoring only the sectors
     unto the root directory, but no further sectors. Also, we want the
     drive X: to be restored to a "clean" state with no errors. If we
     don't delete the RECYCLED folder, then the root directory entry is
     restored, but the "." and ".." entries for this folder are not
     restored and ScanDisk finds errors on the disk. To prevent this
     from happening, we will delete the RECYCLED folder and hence only
     the entry for win386.swp file will be restored.

·

     If DOS' FDISK reports the partition as a "logical DOS drive", it
     has a number of 5 (as in /dev/hda5) or higher.  It is NOT the
     partition labelled "extended" which has a number of 4 or less!!  If
     your Linux fdisk does not display logical partitions, you have a
     broken Linux fdisk (Slackware 2.2 included a broken fdisk, for
     example.)  You can try "cfdisk" if your distribution has it, or you
     will have to get a working fdisk.

·

     When you turn off swapping, Linux has to manage everything in the
     main memory itself. If your system memory is low, say something
     like 16MB, then some large applications that run during
     initialization may not be able to run properly. As an example, you
     may get the following message during initialization:

       Finding module dependencies Out of memory

I don't think this will cause any problems later until you reenable swapping. But it's always better to take some precautions. As you will be seeing in the next section, Linux can also be configured to use a swap file instead of a swap partition. So if you feel that Linux will not run properly with your normal system memory, create a swap file that Linux will use temporarily until swapping is restored. This swap file should preferably in the root directory. Figure out the minimum size of swap space required. It will probably equal to your system memory. Create a swap file of that size by giving the following commands (assuming 16MB swap space):

       # dd if=/dev/zero of=/swap bs=1024 count=16384
       # mkswap /swap 16384
       # sync

Now place the command swapon /swap just after the original swapon -a command in the rc.sysinit file. Thus, now your system has been configured to use swap file and hopefully there will be no Out of memory errors. After having a workable swap partition (i.e after following through this HOWTO completely), you can remove the swapon /swap line that you added to your rc.sysinit file. ·

     Please do not mail me unless you have checked and re-checked that
     you copied your scripts correctly.  More than half of the problems
     reported with this Mini-HOWTO have been due to typos when copying
     the scripts.  (Use cut-and- paste if you can!). Even a spacing
     error can cause an error. For example, if at the startup you get
     the messages

       Verifying swap space...Linux signature found
       swapon: /dev/winswap invalid argument

Then, surely there has been a typing mistake in your scripts. Please check your scripts.

·

     Sometimes, the swap partition is detected to have neither Linux nor
     Windows info and the "No signature found" error appears. I exactly
     don't know why this happens, but for that case, I have written the
     code in swap????.sh files to try six times before reporting an
     error. Normally, the DOS signature should be found on the first
     try, but many a times on my system it is found on iteration 2, 5 or
     not at all after 12 iterations. You may consider increasing the
     number of tries to some value like 12 or 24, there is no harm in
     doing so. Once on my system, the script could not detect the
     signatures even after 50 iterations !  If such a situation arises,
     you may consider making a symbolic link to the swapinit.sh file in
     your root home directory, and execute it at startup.

       # ln -s /etc/rc.d/init.d/swapinit.sh swapinit.sh
       # ./swapinit.sh

However, what I have observed is that once the setup runs on your system for some time, the appropriate signatures are always found on the first iteration.

·

For added reliability

     Your Linux Box runs something very important, or your system memory
     is less so that without swapping, your applications just start
     collapsing ? You have set up the swap partition to be shared by
     Windows. But many a times, your system is unable to detect the
     proper signatures after exhaustive probing and so disables any
     swapping partitions. At your own risk, you may consider removing
     the signature checking logic, but here is a more approachable
     solution.

     First refer to the ``previous point'' and create a swap file in the
     Linux root directory, with the name /swap. Keep it's size according
     to your requirement. Now open the swapinit.sh file and modify the
     last if statement as follows:

       if [ $activated -ne 1 ] ; then
         echo "Swap signature not found after $loopcount tries"
         echo "Activating swap file"
         swapon /swap
         exit 1
       fi

Thus if we find that swap partition lacks appropriate swap signatures, then we enable the swap file. Since the swap file is on the root partition and the Linux Kernel refuses to proceed until it mounts the root file system, you are safely assured that the swap file will always be successfully activated. Instead of creating and keeping the swap file and wasting disk space, you may also modify the code to create the swap file on the fly.

·

     Saving more disk space As we saw, Linux and Windows can share their
     swap spaces. But Window doesn't really require as large a swap file
     as your Linux swap partition ? Then you can have some free space on
     the swap partition (keep the Windows swap file size smaller than
     the swap partition size). Swapping for Windows based applications
     is managed by Windows itself. But many DOS programs like Turbo C++
     Compiler, Norton DOS etc. also manage their own swap files. In that
     case it is possible to configure these programs so that they create
     their swap files in the swap partition instead of their default
     location.  This will increase your usable disk space. Also, most of
     these program forget to delete the swap files they created, leading
     to a large used disk space. But with this setup, every time you
     shut down Linux, you get a clean swap partition, saving your time
     in finding and deleting these swap files.  For example, you can
     tell Turbo C++ to swap on drive say E: by invoking it as

       C:\CLAN>TC /RE

For Norton DOS, set the variable in the NDOS.INI file as,

Swapping = E:\

Many other programs may rely on the TEMP or TMP environment variables to decide where they will swap. In that case you may set these vari­ ables appropriately in your AUTOEXEC.BAT file.

·

      What if the swap partition is a FAT32 ?  No, you can't have a swap
     partition with a FAT32 file system. First of all, Linux can use a
     maximum of 128MB of swap space on a single swap partition.  Thus,
     if your swap partition is larger than 128MB, you are wasting your
     disk space. And Windows will refuse to convert a partition of 128MB
     into a FAT32 file system.

·

     The new style swap space Linux knows about two styles of swap
     areas, the old style and the new style.  By default, you will be
     using the old style swap space with a signature "SWAP-SPACE". If
     you want to use the new style swap space, then first of all change
     "SWAP-SPACE" in all the above scripts to "SWAPSPACE2". Also add an
     option -v1 in the mkswap command in the swapinit.sh script, as
     follows

       /sbin/mkswap -v1 /dev/winswap YYYYY

Also, run the following commands from the shell prompt :

       # swapoff /dev/winswap
       # mkswap -v1 /dev/winswap YYYYY
       # swapon /dev/winswap

It seems that under new style swap space, your usable swap partition can be as large as 2GB on i386 platforms. This means that you can now have a swap partition larger than 512MB which Windows can format as a FAT32 partition . Someone help on how do we save the "Total Special Sectors" under a FAT32 partition.

·

     For users of WINE WINE <http://www.winehq.com> is a program which
     allows running Microsoft Windows programs on Linux. If you are
     using WINE on a system that has been set up to share swap
     partition, then when running a Windows program a win386.swp file of
     about 8kb is created in your Windows folder. This is because the
     swap file on X: is not available at that time. You can safely
     delete this file once you finish running your Windows programs.

8. What are we exactly doing ?

·

     Both Windows and Linux use swap space. When an OS is shut down, the
     contents of the swap space are just garbage, the OS doesn't bother
     about what is in it.  Now what is the point in devoting a 60MB
     partition for swap space to Linux and about 32MB of disk space
     separately to Windows when only one of them is going to run at a
     time (It is possible to run both Linux and Windows at the same
     time, thanks to VMWare. For more information, see VMWare website
     <http://www.vmware.com>). So we want Linux and Windows to share the
     same hard disk space as swap space.

·

     The problem is that Linux uses a partition as a swap space and
     Windows uses a file as a swap space. ( Although it is possible to
     create a swap file for Linux, it is not recommended. See "Linux
     Installation and Getting Started" by Matt Welsh). Now if Linux uses
     the same partition on which Windows stores it's swap file, it will
     overwrite the boot sector, FAT and other data tables that Windows
     assumes to exist on every drive. Thus, Windows will not be in a
     position to find the swap file on startup and will create the
     win386.swp file in the windows directory. Thus, even if by chance,
     your Linux crashes, Windows will be in a position to start. In such
     a case ( with Windows swap file in the  Windows directory), just
     restore the DOS/Windows swap info by restarting Linux and the start
     Windows. Now Windows will be using the swap file on drive X: so you
     can safely delete the win386.swp file in the windows directory.

·

     The remedy is to store those critical data tables once on the Linux
     partition in some file. Then every time Linux starts, check whether
     the swap space was last used by Linux or Windows (using the label
     you gave to your partition).  If it was Linux, just enable swapping
     else first make a swap partition on the X: drive using "mkswap
     /dev/winswap" and then enable swapping.

·

     When you shut down Linux, it is important to restore the swap
     partition to the DOS format, so that Windows can start properly.
     For that purpose we add the

       /bin/zcat /etc/winswap.gz > /dev/winswap

command to the halt file.

9. The swapinit.sh script

This shell script initializes the swap space on the partition. The code for signature detection has been repeated 6 times because many a times the signature is properly detected only on the second or the third try.

(Adapted from the original Swap-Space-HOWTO by H. Peter Anvin)

       #!/bin/sh
       #
       # swapinit.sh - activate the swap partition
       #
       # written by Rahul U. Joshi
       # Verify and initialize swap space
       #

       echo -n 'Verifying swap space... '

       loopcount=0

       # flag to indicate whether the partition has been activated or not
       activated=0

       # check for signatures 6 times before giving up
       while [ $loopcount -lt 6 ]
         do

         if [ "`/bin/dd 2>/dev/null if=/dev/winswap bs=1 count=10  skip=4086`" = 'SWAP-SPACE' ]; then
           echo "Linux signature found, iteration $loopcount"
           echo "Activating swap partitions"
           swapon /dev/winswap
           activated=1
           break

         elif [ "`/bin/dd 2>/dev/null if=/dev/winswap bs=1 count=11 skip=43`" = 'SWAP SPACE ' ]; then
           echo "DOS signature found, iteration $loopcount"
           echo "Making swap partition"
           mkswap /dev/winswap YYYYY
           echo "Activating swap partitions"
           swapon /dev/winswap
           activated=1
           break

         else
          let loopcount=loopcount+1
         fi

         done

       if [ $activated -ne 1 ] ; then
         echo "Swap signature not found after $loopcount tries"
         echo "No swapping partitions activated"
         exit 1
       fi

10. The swaphalt.sh script

This script first checks the Linux swap signature and then restores the Windows file system on it.

(Adapted from the original Swap-Space-HOWTO by H. Peter Anvin)

       #!/bin/sh
       #
       # swaphalt.sh   This file is executed through the /etc/rc.d/init.d/halt
       #               script after swapping and accounting has been turned off.
       #
       # Author:       Rahul U. Joshi
       #

       # check swap partition signature and restore Windows swap info

       loopcount=0

       # flag to indicate whether the swap info has been restored or not
       restored=0

       # check for swap signature 3 times before giving up
       while [ $loopcount -lt 3 ]
         do

         if [ "`/bin/dd 2>/dev/null if=/dev/winswap bs=1 count=10 skip=4086`" = 'SWAP-SPACE' ]; then
           echo "Restoring DOS/Windows swap info , iteration $loopcount"
           /bin/zcat /etc/winswap.gz  >  /dev/winswap
           restored=1
           break
         else
           loopcount=loopcount+1
         fi

         done

       if [ $restored -ne 1 ] ; then
          echo "Swap signature not found after $loopcount tries"
          echo "Skipping restoring"
       fi

11. The msinfo.sh script

This shell script analyses the boot sector of the given partition and displays some information along with the "Total Special Sectors" in a message box. It assumes that the filesystem on the given partition is a FAT16. If not, it will print an error message and exit. Invoke it as

# msinfo <partition name>

To run this script, you will need the "dialog" program that displays dialog boxes. You can get it from here <http://sunsite.unc.edu/pub/Linux/utils/shell>.

#!/bin/sh
#

  # msinfo.sh           This shell script displays the boot sector of the
  #                     given partition.
  #
  # Author:             Rahul U. Joshi
  #
  # Modifications       Removed the use of expr and replaced it by the let
  #                     command.

#
# ------------------------------------------------------------------------ # This program is a free software, you can redistribute it and/or modify # it under the eterms of the GNU General Public Liscence as published by # the Free Software Foundation; either version 2 or (at your option) any # later version.
#
# This program is being distributed in the hope that it will be useful, # but WITHOUT ANY WARRANTY without even the implied warranty of # MERCHANTIBILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General # Public Liscence for more details.
# -------------------------------------------------------------------------

check for command line arguments
if [ $
-ne 1 ]; then

     echo "Usage: msinfo <partition name>"
     exit 1

fi

# check whether the input name is a block device if [ ! -b $1 ]; then

     echo "msinfo: $1 is not a block device"
     exit 1

fi

# create two temporary files for use
TMPFILE=`mktemp -q /tmp/$0.XXXXXX`
if [ $? -ne 0 ]; then

      echo "msinfo: Can't create temp file, exiting..."
      exit 1

fi

TXTFILE=`mktemp -q /tmp/$0.XXXXXX`
if [ $? -ne 0 ]; then

     echo "msinfo: Can't create temp file, exiting..."
     rm -f $TMPFILE
     exit 1

fi

backtitle="`printf "%78s" "msinfo, Information about FAT16 filesystem -- Rahul Joshi"`"

dialog --title "Boot sector of $1" --backtitle "$back_title" \

--infobox "\nAnalysing boot sector for $1\nPlease wait..." 14 60

# truncate TXTFILE to zero length
echo > $TXTFILE

# get Formatting DOS version
dd 2>/dev/null if=$1 bs=1 count=8 skip=3 | dd 2>/dev/null of=$TMPFILE printf >>$TXTFILE "%30s : %s\n" "Formatting DOS version" "`cat $TMPFILE`"

# get file system
dd 2>/dev/null if=$1 bs=1 count=8 skip=54 | dd 2>/dev/null of=$TMPFILE printf >>$TXTFILE "%30s : %s\n" "Filesystem" "`cat $TMPFILE`"

# check if filesystem in a FAT16
if [ "`cat $TMPFILE`" != "FAT16 " ]; then dialog --title "Boot sector of $1" --backtitle "$back_title" \

--infobox "\nCan't find a FAT16 filesystem on $1" 14 60 exit 2
fi

# get volume label in boot sector
dd 2>/dev/null if=$1 bs=1 count=11 skip=43 | dd 2>/dev/null of=$TMPFILE printf >>$TXTFILE "%30s : %s\n" "Volume label in boot sector" "`cat $TMPFILE`"

# get Sector size
dd 2>/dev/null if=$1 bs=1 count=2 skip=11| od -An -tdS | dd 2>/dev/null of=$TMPFILE printf >>$TXTFILE "%30s : %d\n" "Sector size" `cat $TMPFILE` sector_size=`cat $TMPFILE`

# get Reserved sectors
dd 2>/dev/null if=$1 bs=1 count=2 skip=14| od -An -tdS | dd 2>/dev/null of=$TMPFILE printf >>$TXTFILE "%30s : %d\n" " Reserved sectors" `cat $TMPFILE` reserved_sectors=`cat $TMPFILE`

# get FAT sectors
dd 2>/dev/null if=$1 bs=1 count=1 skip=16| od -An -tdS | dd 2>/dev/null of=$TMPFILE fat_count=`cat $TMPFILE`

dd 2>/dev/null if=$1 bs=1 count=2 skip=22| od -An -tdS | dd 2>/dev/null of=$TMPFILE sectors_per_fat=`cat $TMPFILE`

# calculate the no of sectors allocated for FAT's let fat_sectors=fat_count*sectors_per_fat

printf >>$TXTFILE "%30s : %u (%u x %u) \n" "FAT sectors" "$fat_sectors" \

"$fat_count" "$sectors_per_fat"

# get root directory sectors
dd 2>/dev/null if=$1 bs=1 count=2 skip=17| od -An -tdS | dd 2>/dev/null of=$TMPFILE root_sectors=`cat $TMPFILE`

# calculate the no of sectors allocated for root directory let root_sectors=root_sectors*32/sector_size

printf >>$TXTFILE "%30s : %u\n" "Root directory sectors" "$root_sectors"

# get Total special sectors
let total=reserved_sectors+fat_sectors+root_sectors printf >>$TXTFILE "%30s : %u\n" "Total special sectors" "$total"

# display the information
dialog --title "Boot sector of $1" --backtitle "$back_title" --msgbox "`cat $TXTFILE`" 14 60

# delete temporary files
rm -f $TMPFILE
rm -f $TXTFILE

# end of msinfo.sh

12. The original msinfo file

Here is the msinfo file required to find the "Total Special Sectors". It was included by the original author of this HOWTO in an encoded form. First copy the text from the line "begin 755 msinfo.gz" to the line "end" into a temporary file say temp.uu. Then uudecode this file, and finally gunzip to get msinfo file.

       # uudecode temp.uu
       # gunzip  msinfo.gz

Now run the program using the command

# ./msinfo /dev/winswap

The program displays the boot sector information for given partition as well as the "Total Special Sectors" for the drive.

       begin 755 msinfo.gz
       M'XL(`$$YNRT"`Y557TQ;51@_MW]HZ0AM'"$U-.28W([..>84%1%D2QH>',9*
       M2S&VC);V=FV]T*;WWBD+1I)K'YH;DOJFYH80GPR^J""D"R8-K('MS2;QS
       M%Y,E-P&592A$V:[?.;?M"FP/?DG/G^_[?7_Z_3G7PL313TT(?8P0<J"CI':8
       M$5H^:=5<KT^MQ`^UAQ1OQUH0<.]B7S/FC[U!98Y;))]<N^AG"^LB((J%E
       MAFIM[A9U0O`;%:7N[L%G!_-IH34V(J,WUZ.CK%O6IN4DTE,E-144Q-7T)
       M>]_PX\M<3@!`'ZZ26[`-I7A.F!%$;JK.;21`!.\-,5A/CK)\=B3FL:3F8PH
       M<$QDSO91Q%^>L%"Z@KW"-NR3;""5SN,A?'NI[0=P0Q=[P&&$5@3UNZ3VW
       M=-(V`NYQ/)6CX)DC2F`KD!&C/!:R7"Q%]L-6`8'D+=]8T^$V8@RR\;5\P9(
       M^;\&T:F]E`Q`EI,_6YHCZBTBJ09M0VV9!:XVKLF]0NX%'Z4R];\W](3A-%J
       MI:`_&12!>@33QC0S'V8]?O5+0`;3UC23K)!"?@97N8R:29MF/>R)PI>UJF)
       MK%/-4QR39OSJE8,8MHZ)UC`?1ZX'N!ZU`L'X;@.?X["C<1DUT%,9QW32C''
       M"<98PQR8=(L'>96NQWR/4W1@>H3\'!OC3,MMN_"[,=A1OVK^XEH($[$S^H
       MY@28=MB78-$/`=8)(L=\P*$5I_LS@)_G7!=\Z9V@F"``Y$XQM[T!T>(WHNU
       M/T9CH)YIZI("&9ZK32AR=DTN/QNZ."&7?27H_<(=_^=Q"U1N3Y.>!-E`$BY(
       M;(4ZG)/[\_0F_54HY7\5[<!33)\2M%:Y(.THX_N%K?%2L9&(O=4>8F^@IV9(
       M,<HEDU:17T'23M)GAANW-<F'J5-]>6!G2;BU+YN)@<RL.JBIFD4[:<##UG
       MO3Z77WO?L?O+@@G\+(-<"X&QT"&_N7@_\2;JGAEF&U1`JRZCD/Z]7HJ'ZH
       M09_JNAZGJ^N?X5.39_AXMY!!?3@6G>X2,9^)QG%\!IZ@5`SSJ>EWN!SN>HCK
       MLJ%F08RJ5B4YV=T0-R&JUYJW>4"7/D,0/GG`0ZI@__`;6->]K!>C[<GD
       M31/IQP>:!B]D?DT,*<;Y6=9Y]3:P][^W`?+>8F(1!ZY7B1:BN=@D_XY9?0I
       M'?ZT0=V@BBWIIV$47Y@7-,9Q>0<=7;NMW-NS2>9_X3V)8()?A$;!`ALRW
       M&\%RO_^@9F6TP<]'M8J@'AFA"[JM]0(WCQ!`[.826!F&A@HG4JWU5R_KKL&
       M9GNQF$;J[?NZ\YUZ?B].C,OEWI*\94J`:6LB?U,RK^2.([0QRQK(W!D2[K5M
       M,G>&0B7A'K03F"'17*&L9XU@+U2L9K4-GCIG(K(NE:SM,>SM,?;X,T:&U6,
       MT./E%NAUTNE_$,^E(A0M!B7K[D'>X6'\FC25Q3W=+V3YLR^CXJW.S0>#54*
       MZE^AI+N-35^_>![U4!?@VQ%ET<L!BC>MC5"\GH->"T6'4/2NS>((N0,DT>_
       9K6^!S%65KRS`,`,UVB43\!]-BKG]B`<``#5"
       `
       end

13. Acknowledgements, feedback and dedication

This Mini-HOWTO has been largely derived from the Swap-Space Mini HOWTO by H. Peter Anvin. Rahul.U.Joshi added the Windows 95/98 specific details as well as a few Red Hat Linux specific details. The msinfo program given in the original HOWTO didn't work on the Joshi's Red Hat Linux 6 system, so he created a similar program. However, He has also included the original msinfo program.It is now maintained by Rahul Sundaram.

I rely on you, the readers, to make this HOWTO useful. If you have any suggestions, comments, corrections, requests, flames, etc., feel free to contact Rahul Sundaram <mailto:rahulsundaram AT yahoo DOT co DOT in>. I dedicate this document to my friends.


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