How do you mount ISO file on Linux using the CLI and GUI app? First, try to understand an ISO image. It is an archive file (disk image) of an optical disc using a conventional ISO (International Organization for Standardization) format. ISO image files typically have a file extension of .ISO. The name “ISO” comes from the ISO 9660 file system used with CD-ROM or DVD media, but an ISO image can also contain UDF file system because UDF is backward-compatible to ISO 9660. You can mount an ISO file or images via the loop device under Linux. It is possible to specify transfer functions (for encryption/decryption or other purposes) using loop device. This page explains how to mount ISO files on Linux.