Rescue Me!

Ever been caught without that rescue disk, and thought that everything was lost, and that you have no choice but to reinstall the operating system? Well don’t do it just yet. In this article we’ll introduce you to tomsrtbt, a bootable diskette that will allow you to salvage and/or repair files regardless of your operating system. (This article originally appeared in the April 2004 issue of Plug-In).

Apple has done away with it for years now. My BIOS scornfully refers to it as a legacy device. Yes, I’m talking about the poor 3.5-inch floppy. It wasn’t always so. There was a time when the 3.5-inch reigned supreme. It was much superior to the 5.25-inch– especially if you remember the 1541 Commodore external drive. I still shudder at the thought. And then there was the cassette tape that you used with the ZX-81. (Now I’m really showing my age!)

In any case, I recently had occasion to be very thankful for this legacy device. My dual boot Win2K/Linux Red Hat 7.1 wouldn’t boot into Linux any more; probably something to do with that SCSI card I recently added. “Well,” I thought, “it’s simple enough to use my Linux boot disk and see if I can sort out the problem.” But no such floppy could be found.

Allow me a quick aside to Windows-only readers. Don’t change the channel. There is something here for you, because even though the Windows operating system can’t view a Linux partition, Linux can see Windows. I’ll let you draw your own conclusions about this fact, but one thing this means is that you can use Linux to salvage or repair Windows files.

To get back to our main problem, and to paraphrase an old expression, it looked like I was “up the effluent stream with no means of propulsion.” Okay, so I could boot from the installation CD. But in the spirit of not forgetting an auld acquaintance, let’s see what we can do with only a floppy drive. Besides, as you’ll see, an irresistible temptation presented itself to me along the way.

{mospagebreak title=Creating a Bootable Diskette}

In the frantic search for my Linux Red Hat 7.1 boot disk, I came across a vaguely remembered diskette labelled “tomsrtbt 2.0.103.” Could Alice resist the bottle labelled Drink Me?

To answer that question you really need to know what tomsrtbt is (pronounced “Tom’s Root Boot”). To quote Tom, tomsrtbt stands for: “Tom’s floppy which has a root file system and is also bootable.” I had my boot disk ready-made, but you will have to create yours by going to http://www.toms.net/rb/.

Locate the link for downloading, find an appropriate mirror and choose the file named “tomsrtbt-2.0.103.dos.zip” if you wish to create your diskette under Windows, or “tomsrtbt-2.0.103.tar.gz” for Linux/Unix.

A word of warning at this point: if you are running Windows 2000, creating this diskette is a bit problematic. If you have a Windows 98 machine handy this provides your easiest solution. Copy the zipped file to this machine, decompress it and boot into DOS to create your bootable floppy. Otherwise see http://not.toms.net/twiki/bin/
view/Tomsrtbt/CreateTomsrtbtFromWin2000
. Various solutions are presented there, but the next easiest seems to be to make DOS boot disks using the resources at http://www.bootdisk.com and then create your Linux diskette.

A couple of final notes: This distribution of Linux does not support writing to the NTFS file system, but check Tom’s site for any updates. There should be no problems creating your bootable disk under Linux.

{mospagebreak title=Booting From a Legacy Device}

Let’s assume that you have managed to create your Linux boot diskette. Reboot using this diskette, first making sure your BIOS is set to boot from the floppy drive.

Okay, I know it’s taking a long time to load the operating system but go ahead and use the time to reflect on that auld acquaintance– and be comforted that you are not using a 5.25” drive.

Choose your language — yes, you get to choose your language if you don’t want the default; pretty soon you’ll be looking at a screen full of all the Linux commands available. If you’re a little shaky at the command line in Linux or you are one of the fearless Windows-only users who has followed us this far don’t worry. The operating system commands you need are limited in number and we’re going to explain them as the need arises.

At this point you can remove the diskette from the drive. You don’t need it any more because you are now running from a RAM drive. Besides, you may want to format a diskette (Linux or Windows) and copy files to this drive. That blinking cursor wants you to log in. Your only choice is to enter root and after that the password, xxxx.

“ls” and “cd” Commands

The most basic command you’ll need is ls, the Linux equivalent of the DOS dir. Try it out and you should see a list of directories (folders in Windows terminology). If you want to see more information about these directories then type ls –l. The -l is a switch that gives the “long” view of your files.

Next, you will want to navigate around the file system and for this you’ll need cd. Looks familiar doesn’t it? In fact, it works exactly the same way as it does under DOS. Use cd with a directory name and that directory will become your working directory. Returning to the parent directory is as simple as cd .. or to go to the root directory cd /. Don’t forget the space, or it won’t work.

{mospagebreak title=Mounting a Drive}

By now you are probably itching to look at your Windows file system, especially if you’ve never seen it from Linux before. To do this, the file system needs to be mounted, and in order to be mounted it needs a mount point. What this boils down to is that you need to create a directory and mount a specific file system on this directory. It is conventional to create mount points in the mnt directory. If you are at the root directory and issue the command ls you should see this directory. Make it your working directory by typing cd mnt. You’ll find that there are no subdirectories here but we are going to make one. Again the command is identical to the DOS command. Type mkdir cdrive and press Enter. Now list the contents of the current directory to see the newly created directory. There you go. You’ve created a directory that will be the mount point for the Windows file system.

Please remember, though, that you are working with a RAM drive, so the changes you are making and directories you are creating won’t be there the next time you boot from the diskette.

At this point you need to know something about the way that your hard drive is organized. If you are only running Windows and have not partitioned your drive then your C: drive will be referenced from Linux as hda1 and the command to mount this file system is mount /dev/ hda1 /mnt/cdrive –t msdos. Try it. You’ll only see a message if you’ve made an error. Now change directories to the /mnt/cdrive directory. Not sure where you are? Determine your present working directory by typing pwd. To look at your Windows files you simply need to change to the /mnt/cdrive directory and use the ls command. Savour the moment if this is the first time that you have seen a Windows partition from Linux.

If you are running Linux then I’ll assume you know which drive to mount. Again, if you only have one partition then it will be hda1.

You should always unmount a drive when you are finished. Your C: drive would be unmounted by typing umount /dev/hda1. Make sure the drive you are trying to unmount is not your present working directory or you’ll get a “drive busy” error.

{mospagebreak title=Copying Files}

If you’re here to salvage some files by copying them to a diskette then you will also need to know how to mount and format a floppy. You’ll be able to format your diskette for DOS or for Linux by first typing fdformat /dev/ fd0H1440. To make a Linux floppy type then type, mke2fs /dev/fd0 or, alternately, mkdosfs /dev/fd0 for a DOS diskette. To copy files to your floppy you will again have to mount the drive. This can be done in exactly the same way that any other drive is mounted. First create a mount point, let’s create one called “floppy”, and then mount the drive by typing mount –t msdos /dev/fd0 /mnt/floppy. Just drop the file type switch (–t msdos) if you are mounting a Linux floppy. We’re now ready to copy files.

Copying files is identical regardless of the operating system. You simply use the cp command specifying a source and destination. For instance, to copy the file fstab in the etc directory to your floppy you would simply type cp /etc/fstab /mnt/floppy/fstab. If you wish to copy a directory and all its contents then you will need to know the -r switch. The “r” stands for recursive and will copy all files and directories within the directory specified.

In this way you can salvage as many files as needed from the hard drive. Read on for more advanced commands.

Advanced Commands

In some cases you may want to run as root on your original Linux partition. This can be done by creating a mount point for the file system, mounting it and then using the chroot command. This is exactly what I wanted to do so that I could make a boot disk for my Red Hat 7.1 installation.

First I created a mount point for the file system. In my case I knew that my Linux drive was device hda5 so I created a mount point called “rh71”, mounted this device and then simply typed the command chroot /mnt/rh71. I next changed my directory to the sbin directory, typed ./mkbootdisk –device /dev/fd0 2.4.2-2 and inserted a floppy into the drive. The number following the device is the kernel version number of my distribution. You don’t have to remember it–you can easily look it up by examining the files in the “boot” directory.

When I was finished I changed back to tomsrtbt by typing exit at the command line.

In very quick order, I had a boot disk for my Red Hat installation. I could now boot into Linux and do anything else I needed to do using X Windows.

Things don’t always work out so nicely though. Sometimes you may need to look at or change information in a file. In this case you will have to use the text editor vi. I’ll give you some quick tips on using this editor.

To invoke vi, type vi and pressing Enter. If there is a specific file that you wish to edit, type the name of the file after the command vi. Upon start-up, vi is in command mode and you need to press i for “insert” if you wish to add to or change the file. Saving your changes is done by returning to command mode by hitting the Esc key, followed by :wq. This is not an extended tutorial on using vi, so if you have made mistakes and want to abandon what you’ve done you may quickly exit by pressing the escape key and then :q!. None of your changes will have been saved.

There are many more useful commands available–for checking the integrity of the file system, for instance–but you would probably do well to learn a little more about Linux before exploring them. You don’t want to accidentally reformat your drive!

Conclusion

The “tomsrtbt” distribution is a nice little tool if you have trouble booting from your hard drive and don’t have a rescue disk. Using a few basic Linux commands, files can be examined, copied or changed regardless of what operating system you are running.

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