I have two somewhat older computers, an HP laptop running Ubuntu Gutsy Gibbon and a custom desktop running Debian Lenny. They are not networked, and I do not have home internet access since I recently moved to an area where broadband is not available and I have a winmodem. I am trying to upgrade the system on the laptop, but have run into a strange problem. I have downloaded a copy of the Xubuntu Karmic Koala iso from a public wifi spot onto the laptop. The laptop does not have a CD burner, so I am attempting to transfer the image to the desktop computer via a usb device. The problem is that it will not transfer accurately. The md5sum of the iso is fine on the laptop hard drive and also after I have copied it to the usb device. I unmount the usb device from the laptop, connect it to the desktop, and copy the file to the desktop hard drive, from where I hope to burn the CD. I check the md5sum and it doesn't match. What is even stranger is that if I now check the md5sum of the iso file on the usb drive, that has also changed. The size of the file in bytes remains the same, but when I ignored the md5sum and tried to burn the CD anyway, it would not run, so something is wrong. I have tried this dozens of times with a compact flash card formatted fat16, a thumb drive formatted fat32, and another thumb drive that I reformatted ext2, all with the same result. The md5sums are always different, but always wrong. What I would like to know is, do I have defective hardware, or is something else going on? I have never had a problem transferring other, smaller files in this manner. How else can I get this iso file onto my desktop computer? Thanks to anyone who can help me figure this out.

My guess is that for whatever reason the laptop is not unmounting the usb drive properly. Have you tried the paranoid approach: copy the file to the USB drive, then shut down the laptop. Only once it's fully turned off remove the USB drive and put it in the desktop.

No, I don't think I did try that, but I will. Thanks for the suggestion. However, I don't think that explains why the md5sum of the iso on the usb should be different from that on the desktop after I have transferred the file. Should I also shut down and restart the desktop before checking the md5?