If you need to mount a lot of ISOs on a system than you could run into the problem, that you do not have free loop devices left.
There are several solutions from running “MAKEDEV -v /dev/loop” at boot time (e.g. add it to rc.local) to creating a file called loop.conf at /etc/modprobe.d/ and inserting the follwoing line:
At the end the following parameter has to be added to the Grub-config file:
instead of makedev (which creates 264 loop devices) the following snipped can be used: