In Unix-like operating systems, a loop device, vnd (vnode disk), or lofi (loop file interface) is a pseudo-device that makes a computer file accessible as a block device.
It also provides a permanent segregation of data, for example, when simulating removable media on a faster and more convenient hard disk or encapsulating encrypted file system.
Various Unix-like operating systems provide the loop device functionality using different names.
The management user interface for the loop device is losetup, which is part of the package util-linux.
FreeBSD followed the same conventions as other BSD systems until release version 5, in which the loop device was incorporated into the memory disk driver ("md").
[1] In Solaris/OpenSolaris, the loop device is called "loopback file interface" or lofi,[2] and located at /dev/lofi/1, etc.
The command marry also supports encrypting and decrypting of the regular file.
MacOS implements a native image mounting mechanism as part of its random access disk device abstraction.
[5][6] However, the facility is often added using third-party applications such as Daemon Tools and Alcohol 120%.
Freely-available tools from VMware (Disk Mount Utility) and LTR Data (ImDisk) can also be used to achieve similar functionality.