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File systems


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.

# 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


COW (copy on write) file system

The cow filesystem was found on xubuntu live CD. See

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