Backup USB Jump Drive to Disk Image

I recently had the need to create a backup image of a portable USB device to store for safe keeping. This was not a bootable drive, just a drive with files on it. Yeah, I could have copied the files from the drive, or I could have create a zip archive from them. But I wanted to create an image as I wasn’t really sure of the contents of the drive. It was an update stick for a Golden Tee GO arcade machine (see Repairing a Golden Tee Go Arcade).

Create the Backup

1. Find the source device with lsblk (you could check dmesg or disk utility or any other method)

    root@desktop:/home/sam# lsblk
    NAME                   MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINT
    sda                      8:0    0 232.9G  0 disk  
    ├─sda1                   8:1    0   243M  0 part  /boot
    ├─sda2                   8:2    0     1K  0 part  
    └─sda5                   8:5    0 232.6G  0 part  
    └─sdb5_crypt         253:0    0 232.6G  0 crypt 
        └─desktop--vg-root 253:1    0 232.6G  0 lvm   /
    sdb                      8:16   1  28.8G  0 disk  
    └─sdb1                   8:17   1  28.8G  0 part  /media/sam/A38A-3083
   

2. Create the backup using dd

    dd if=/dev/sdb of=/home/sam/gt-go.img bs=4M status=progress
   

3. Store the image for safe keeping

Mount the Image

The following describes how to mount the image (read only in this case) and retrieve files from it.

1. Find the block size and offset

    fdisk -l /home/sam/gt-go.img 
    Disk /home/sam/gt-go.img: 28.82 GiB, 30943995904 bytes, 60437492 sectors
    Units: sectors of 1 * 512 = 512 bytes
    Sector size (logical/physical): 512 bytes / 512 bytes
    I/O size (minimum/optimal): 512 bytes / 512 bytes
    Disklabel type: dos
    Disk identifier: 0x647fdcd9
   
    Device               Boot Start      End  Sectors  Size Id Type
    /home/sam/gt-go.img1       2048 60437491 60435444 28.8G  b W95 FAT32
   

   In this case the block size is 512 and the offset is 2048

   Could also use the file command to find the start sector

    file /home/sam/gt-go.img 
    /home/sam/gt-go.img: DOS/MBR boot sector; partition 1 : ID=0xb, start-CHS (0x1,0,1), end-CHS (0x346,31,20), startsector 2048, 60435444 sectors, extended partition table (last)
   

2. Calculate the offset using block size and start sector from above

    512 * 2048 = 1048576
   

3. Mount the image

    mkdir /mnt/iso
    mount -o ro,loop,offset=1048576 /home/sam/gt-go.img /mnt/iso
   
    ls -l /mnt/iso