Error While Mounting an ISO Image in Linux: ioctl: LOOP_SET_FD: Invalid argument

I recently received this error while mounting an iso image in a CentOS 5.3 install:

[root@host ~]# mount -t iso9660 -o loop /mnt/glusterfs/ecp-spe-4867.iso /mnt/iso/
ioctl: LOOP_SET_FD: Invalid argument

For more detail:

[root@host ~]# mount -v -t iso9660 -o loop /mnt/glusterfs/ecp-spe-4867.iso /mnt/iso/
mount: going to use the loop device /dev/loop0
ioctl: LOOP_SET_FD: Invalid argument
mount: failed setting up loop device

So what could this mean? The confusing error message “ioctl: LOOP_SET_FD: Invalid argument” means that your ISO image is on a filesystem that is not supported for the loopback device on your system. In my case, that was a GlusterFS mount that was hosting the image.

I copied it into another directory on my root ext3 filesystem and it mounted just fine!