From: https://trailofbits.github.io/ctf/forensics/
Occasionally, a CTF forensics challenge consists of a full disk image, and the player needs to have a strategy for finding a needle (the flag) in this haystack of data. Triage, in computer forensics, refers to the ability to quickly narrow down what to look at. Without a strategy, the only option is looking at everything, which is time-prohibitive (not to mention exhausting).
Example of mounting a CD-ROM filesystem image:
mkdir /mnt/challenge
mount -t iso9660 challengefile /mnt/challenge
Once you have mounted the filesystem, the tree command is not bad for a quick look at the directory structure to see if anything sticks out to you for further analysis.
You may not be looking for a file in the visible filesystem at all, but rather a hidden volume, unallocated space (disk space that is not a part of any partition), a deleted file, or a non-file filesystem structure like an http://www.nirsoft.net/utils/alternate_data_streams.html. For EXT3 and EXT4 filesystems, you can attempt to find deleted files with extundelete. For everything else, there’s TestDisk: recover missing partition tables, fix corrupted ones, undelete files on FAT or NTFS, etc.
The Sleuth Kit and its accompanying web-based user interface, “Autopsy,” is a powerful open-source toolkit for filesystem analysis. It’s a bit geared toward law-enforcement tasks, but can be helpful for tasks like searching for a keyword across the entire disk image, or looking at the unallocated space.
Embedded device filesystems are a unique category of their own. Made for fixed-function low-resource environments, they can be compressed, single-file, or read-only. Squashfs is one popular implementation of an embedded device filesystem. For images of embedded devices, you’re better off analyzing them with firmware-mod-kit or binwalk.