If you have downloaded a *.iso file from a website (for example, any Linux OS distribution), you can view the content of the iso file without writing as an iso to a CD or DVD as explained below using mount -o loop.. Please note that a loop device is a pseudo-device which will make an iso file accessible to the user a block device.
Syntax: # mount ISOFILE MOUNT-POINT -o loop $ su - # mkdir /tmp/mnt # mount -o loop /downloads/ubuntu-9.04-desktop-i386.iso /tmp/mnt # cd /tmp/mnt # ls -l
For mounting you need to be logged in as root or you should have sudo permission. Read below to find out how to mount iso file as regular non-root user.