Filesystem

squashfs

squashfs is a heavy-compression based read-only filesystem that is capable of compressing 2 to 3 GB of data onto a 700MB. Linux liveCD are built using squashfs. These CDs make use of a read-only compressed filesystem which keeps the root filesystem on a compressed file. It can be loopback mounted and loads a complete Linux env. Thus when some file are required by processes, they are decompressed and loaded onto the RAM and used.

• https://en.wikipedia.org/wiki/SquashFS
• http://squashfs.sourceforge.net/
• http://elinux.org/Squash_FS_Howto
• Ubuntu's snaps use the squashfs filesystem,
  • The snap file format is a single compressed SquashFS filesystem from Introduction to snapcraft.
  • A technical comparison between snaps and debs

# create a squashfs file
sudo mksquashfs /etc test.squashfs 

# mount the squashfs file 
mkdir /mnt/squash
mount -o loop compressedfs.squashfs /mnt/squash
# you can acess the contents at /mnt/squashfs

# exclude files 
sudo mksquashfs /etc test.squashfs -e /etc/passwd /etc/shadow
# or specify a list of exclude files given in a file
cat excludelist  # /etc/passwd
sudo mksquashfs /etc test.squashfs -ef excludelist

Btrfs

• https://en.wikipedia.org/wiki/Btrfs
• Fedora 33 launches with updated GNOME and BTRFS
• Install MX Linux with btrfs partitioning. MX Linux 21: Dual-boot with Windows (& how to completely remove MX Linux and its bootloader) (video, Dec 2021) quite complete!

COW (copy on write) file system

The cow filesystem was found on xubuntu live CD. See http://en.wikipedia.org/wiki/Copy-on-write

How To Protect Your Server Against the Dirty COW Linux Vulnerability (10/21/2016)