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

• Fedora 33 launches with updated GNOME and BTRFS