How a Corrupted USB Drive Was Saved by GNU/Linux
To summarize exactly what fixed the USB device:
Step 1: create a filesystem image of the right size, with FATs and the directory in the right places:
# dd if=/dev/zero of=/tmp/r2x bs=512 count=1001952 # losetup /dev/loop2 /tmp/r2x # mkfs.msdos -n mkfs__msdos -s 16 -R 64 /dev/loop2
Step 2: copy bytes from the corrupt image, except the boot sector, onto the filesystem image created in step 1:
# dd if=r1 of=r2x bs=512 skip=1 seek=1
Step 3: execute filesystem repair on that image:
# fsck.msdos -f -r /dev/loop2
Because I knew that FAT1 was bogus, I told it to use FAT2, and it reported success. It asked me whether to write the changes, and I said yes.
The filesystem images in /tmp/r2x and /dev/loop2 now were consistent. The acid test was to try to mount the filesystem:
# mkdir /tmp/r2d # mount -t vfat /dev/loop2 /tmp/r2d # ls -lRA /tmp/r2d
After which all kinds of good stuff appeared.
Note: A good result to ls -lR showed that I was lucky in one other way: I didn't know if the boot sector had a good value for the size of the root directory, the -r parameter to mkfs.msdos. I simply used the default and it turned out fine.
At this point, I decided I had better burn a CD. I burn and read CDs all the time on Linux, but I rarely burn CDs to be read by Windows. Again I did a Web search, and a page from IBM's DeveloperWorks site turned up. I had searched "linux burn CD windows" or something like that. So I tried this:
# mkisofs -J -r -v /tmp/r2d | \ cdrecord -v -pad -eject fs=4m speed=4 dev=0,0,0 -
I wasn't 100% sure that Windows would like this CD, but fortunately I have Windows95 under Win4Lin. Its sole purpose for me is to run Quicken and TurboTax, but I fired it up and pointed Windows Explorer at the just-burned CD-ROM. Explorer loved it. I used gimp(1) to capture a screenshot and e-mailed the image to my friend's brother--he was ecstatic.
Shell jockeys need not read this.
1 #!/bin/bash 2 # parameters added to mkfs.msdos.... 3 ARGS="$*" 4 if mount | grep /tmp/r2d; then umount /tmp/r2d; fi 5 losetup -d /dev/loop2 6 losetup /dev/loop2 /tmp/r2x 7 mkfs.msdos -n mkfs__msdos -s 16 $ARGS /dev/loop2 8 mount -t vfat /dev/loop2 /tmp/r2d 9 yes hello | dd bs=8192 count=3 of=/tmp/r2d/foo.txt 10 umount /tmp/r2d
Line 1 identifies to exec(2) that this is supposed to be run by the shell. I've become accustomed to bash, the Bourne again shell.
Line 2 simply explains line 3, that the parameters you type after b.sh are parameters to add to the mkfs.msdos command line.
Lines 4-6 establish /dev/loop2 as the block device whose contents are in the filesystem image kept in /dev/r2x. Line 4 unmounts the artificial filesystem if it was mounted; this is done because we're about to make some changes to it. Lines 5-6 make sure that /dev/loop2 is connected to /tmp/r2x and only to /tmp/r2x.
Line 7 creates an artificial filesystem image with whatever additional parameters the user gave--remember $ARGS from line 3?.
Line 8 mounts the filesystem onto /tmp/r2d. Line 9 creates a file of about 24KB (three clusters), so I have a filename to look for at the beginning of the directory.
Line 10 then unmounts the artificial filesystem image, so the kernel does not think there are inconsistencies if I play with /tmp/r2x.
|illusive networks' Deceptions Everywhere||Aug 29, 2016|
|Happy Birthday Linux||Aug 25, 2016|
|ContainerCon Vendors Offer Flexible Solutions for Managing All Your New Micro-VMs||Aug 24, 2016|
|Updates from LinuxCon and ContainerCon, Toronto, August 2016||Aug 23, 2016|
|NVMe over Fabrics Support Coming to the Linux 4.8 Kernel||Aug 22, 2016|
|What I Wish I’d Known When I Was an Embedded Linux Newbie||Aug 18, 2016|
- Download "Linux Management with Red Hat Satellite: Measuring Business Impact and ROI"
- illusive networks' Deceptions Everywhere
- Happy Birthday Linux
- What I Wish I’d Known When I Was an Embedded Linux Newbie
- ContainerCon Vendors Offer Flexible Solutions for Managing All Your New Micro-VMs
- New Version of GParted
- All about printf
- Tor 0.2.8.6 Is Released
- Updates from LinuxCon and ContainerCon, Toronto, August 2016
- Tech Tip: Really Simple HTTP Server with Python
With all the industry talk about the benefits of Linux on Power and all the performance advantages offered by its open architecture, you may be considering a move in that direction. If you are thinking about analytics, big data and cloud computing, you would be right to evaluate Power. The idea of using commodity x86 hardware and replacing it every three years is an outdated cost model. It doesn’t consider the total cost of ownership, and it doesn’t consider the advantage of real processing power, high-availability and multithreading like a demon.
This ebook takes a look at some of the practical applications of the Linux on Power platform and ways you might bring all the performance power of this open architecture to bear for your organization. There are no smoke and mirrors here—just hard, cold, empirical evidence provided by independent sources. I also consider some innovative ways Linux on Power will be used in the future.Get the Guide