Kris Occhipinti filesystem #study

tutorials and comments

#---------- Mounting ISO images linux tutorial ----------#
#http://youtu.be/Tsyk6vLr91k

mkdir mymountpoint
sudo mount ubuntu_or_whatever.iso mymountpoint/
#that's expected that an iso mounted would be write protected/read only =D 
#just like a CD
sudo umount mymountpoint/

#some filesystems need the "-o loop" option
#so the mount is like
sudo mount -o loop ubuntu_or_whatever.iso mymountpoint/


#---------- Linux kernel and initrd Basics tutorial ----------#
# http://youtu.be/boxF9t29xZQ
# a tutorial inspecting different iso images
# commands here are based on Core-current.iso

# first step, mount and continue next steps :D
cd iso/boot

# grub and isolinux are different bootloaders!

# vmlinux is the kernel //name my differ
# to ensure we may use file command with it
# an output of 'blablabla: x86 boot sector' confirms that
file vmlinuz

# cpio some type of archiving
# gzib file: small compressed file, so common that
file core_or_whatever.gz 
# initrd: initial ramdisk ... will follow

cd isolinux/
# Inspect the most important of config files: isolinux.cfg
less isolinux.cfg
# This one told us what the kernel we'll use
# and what initrd we'll use.
# cfg files may include other cfg files for organizing.
# Displayed messages are written in different files and included too.

# kernel is first loaded into the ram, initrd is loaded that makes some other tasks,
# then the main filesystem is loaded replacing the initrd


#---------- Extracting CPIO files on Linux initrd gz tutorial ----------#
# http://youtu.be/SZo6nQZV1bE

# Inspection on Core-current
mv iso/core.gz mytestdir/core.gz
gunzip core.gz
file core
# Will tell us its a CPIO archive!

# Now use the standard cpio program to extract
cpio -i < core
# NOTE: it will give some not permitted operations, as permissions are important,
# but the filesystem will extract :3
# thus we may need to use sudo!

# single step method
zcat core.gz |sudo cpio -i
# zcat is like cat but for gzip files

# get size in human friendly format!
du -h


#---------- Extracting LZMA Files on Linux initrd CPIO ----------#
# http://youtu.be/joOUG8an1O0

# Inspection on Slitaz
# Step 1: mount, get a copy of rootfs4.gz in read/write dir then continue ^_^

# we'll notice that 'gunzip rootfs4.gz' will return 'not in gzip format'
# using the file
file rootfs4.gz
# Its obvious that the .gz extension has nothing to do with it being
# LZMA compressed data

# Uncompress
unlzma rootfs4.gz -S .gz
# use -S to specify the suffix, that's removed to deduce the target name

file rootfs4
# Ensure its CPIO as we expect

sudo cpio -i < rootfs4


#---------- Extracting SQUASHFS files on Linux initrd.gz tutorial ----------#
# http://youtu.be/1mMXzgzHeE4

# Inspection on Mint
# 'unsquashfs-tools' may need to be apt-geted ^_^
unsquashfs myMintMountDir/casper/filesystem.squashfs

# notice that the extraction went into an autogenerated named directory
# so ... for a better naming :D
mv squashfs-root/ mint

cd mint && du -h
#uncompression from 888 to 3.0G :3


#---------- Create a Broken Linux Live CD Tutorial ----------#
# http://youtu.be/hB_Rsx0HGWY

# Create a dir with subdir inside
mkdir -p mylive/iso/isolinux

# mylive: iso file container
# iso: root dir for image //keep clean
# isolinux: save here info for bootloader, kernel and initrd

cd mylive/iso/isolinux

# Get a kernel
cp /boot/vmlinux-x.y-z=amd64 linux
# note: name isn't an issue, as we're gonna keep it consistent with the cfg file

# Get an initrd
cp /boot/initrd.img-x.y-z-amd64 initrd
# note: ensure the x, y and z are the same for kernel as for initrd

## another way to make initrd, not sure how its better!
sudo mkinitramfs -o initrd

# Get the isolinux.bin //don't know why :|
# if syslinux package is installed!
# search example for isolinux.bin
find /usr -name "isolinux.bin"

cp /usr/share/syslinux/themes/debian-wheezy/isolinux-live/isolinux.bin ./

# Make our own config 
vim isolinux.cfg

# display boot.txt
# prompt 1
# default mylinux
# label mylinux
#     kernel linux
#     append initrd=initrd

# Make our own message
vim boot.txt

# =========welcome to mylinux cd =========

cd ../../

# Make the iso
xorrisofs -l -J -no-emul-boot -boot-load-size 5 -boot-info-table -b isolinux/isolinux.bin -c isolinux/boot.cat -o mylinux.iso iso
# "make-iso-fs" or some abbreviation, may be the alternative in older distros
# too many options ... only b was illustrated
# c: another file to be created 
# b: where to find the bin for the boot loader
# l: 
# J: 
# no-emul-boot: 
# boot-load-size: 
# boot-info-table: 

### Why its broken: cause the initrd we put is looking for our filesystem to call :D 
### so it will end up giving us a shell

# Emulation time
# qemu should be apt-geted for that
qemu-system-x86_64 -cdrom mylinux.iso
# we should now see it failing ^_^
# note: usage of 86_64 cause we used a 64bit kernel