Squashfs is a compressed read-only file system for Linux.
[3] It is often combined with a union mount filesystem, such as UnionFS, OverlayFS, or aufs, to provide a read-write environment for live Linux distributions.
The snap package system also uses Squashfs as its file container format.
Since then the Squashfs kernel-space code has been maintained in the Linux mainline tree, while the user-space tools remain on the project's GitHub page.
[15] Linux kernel 2.6.35 added support for extended file attributes.