Live USB "Check disk for defects” finds defects but doesn't list them

Question

I downloaded the iso file for XUbuntu. I created a live usb using Pen Drive Linux. I turned on my computer, booted to the XUbuntu installation screen, and selected "check disk for defects".

A minute later, it says that it found one defect. How do I figure out what this defect is?

Answer 1

“Check disk for defects” will compare the checksums of the files on the USB drive against a known good list. The result means there was an error transferring the Xubuntu live system to the USB drive.

• Did you follow the official instructions to create a bootable USB drive?
• Did you check the integrity of the downloaded ISO image? In case of an error here, re-download the image.

Answer 2

You can check the integrity of the image written to the USB drive by checking it's MD5 sum against the original ISO's checksum:

Check the original ISO's size:

% ls -l archlinux-2015.10.01-dual.iso 

-rwxrwxr-x 1 user user 689963008 nov 22 21:35 archlinux-2015.10.01-dual.iso

$SIZE = 689963008

Run this command, changing $SIZE according to the original ISO's size and replacing /dev/sdc with the actual device path:

sudo dd if=/dev/sdc iflag=fullblock count=$(($SIZE/512)) 2>/dev/null | md5sum -

Check the output against the original ISO's MD5 sum.