I received a USB flash drive that contains a pre-installed ISO 9660 (Joliet) image on it. To delete the image and free up space on the drive, I attempted to use sudo rm -rf /Volumes/ISONAME via a Terminal; however, the command failed as the image is a Read-only file system. How should I go about deleting the ISO?

For reference, I'm running OSX 10.9.5.

Thanks so much!

  • OSX mounted the image as a CDROM. You could use Disk Utility to format this (but that's for the Apple forum -- offtopic here). Mar 10 '16 at 1:39
  • Hi Thomas; Indeed, I first attempted to use Disk Utility for this procedure. Unfortunately, Disk Utility didn't recognize the ISO (i.e., the "CDROM" didn't appear within the application), hence why I considered using a Terminal instead. Mar 11 '16 at 2:13
  • I had in mind that you would reformat the flash drive itself (not rearrange the contents of the ISO). Mar 11 '16 at 2:15
  • Yep, I endeavored first to use the "Erase" option in Disk Utility to clear then reformat flash drive. Erasing the drive did nothing to the ISO, though; and since the ISO / CDROM didn't even appear in Disk Utility, I was perplexed on my next steps. Mar 11 '16 at 2:18

The large ISO file is just one file on the USB drive. Your computer may simply have mounted the ISO as a filesystem (like a real CDROM). In that case the mount command would show you this.

To really free up space, you might want to simply reformat the USB drive, making an empty filesystem.

The way to go with OSX is using Disk Utility, which can be used to format a variety of removable devices (as well as your computer's disks).

Here are a few useful links:


Firstly unmount the disk and note the device, eg. /dev/sdc1

Post that you have a number of options like, - dd (CLI based, be very CAREFUL) - gparted (GUI based)

  • Duly noted; I'll give these options a shot. Thanks! Mar 11 '16 at 2:14

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