Convert bootable USB to ISO file

Solution 1:

To create an image from a drive

sudo dd if=/dev/sdx of=/path/to/new.iso

Alternatively, to create a USB drive from an image

sudo dd if=/path/to/iso of=/dev/sdx

Replace /dev/sdx with your USB drive, e.g. /dev/sdc.

WARNING: It is imperative that you make certain you are using the correct drive. If you don't use the correct drive, you could lose your data. To check your currently mounted drives, use the command lsblk.

Note: Copying large files (1 GB or higher) can take a long time, be patient.

Solution 2:

Another option is to use gnome-disks.

You can start if from a terminal with gnome-disks or look for the application Disks in the Dash.

Once the USB stick is mounted, select it and use the more actions icon to choose Create Image.

Disks is a GUI for the same command.