mergeusb

#!/bin/bash

if [ "$1" == "" ]
  then
    echo "Usage $0 /path/to/mountedUSBDrive"
    exit 1
fi

# adding a trailing / here so we don't accidentally start with / later on
usbpath=$1/
#check for root
#look up disk space requirements from usb and check
#check for mksquashfs and prompt to install squashfs-tools
#option for making safer by copying from usb 1st to make a backup

cd /var/tmp
mkdir usblive
cd usblive
mkdir readonly readwrite merged
echo "Mounting ${usbpath}casper/filesystem.squashfs"
mount ${usbpath}casper/filesystem.squashfs readonly -t squashfs -o loop,ro

echo "Mounting ${usbpath}casper-rw"
mount ${usbpath}casper-rw readwrite -o loop,rw
echo "Mounting overlayfs"
mount none merged -o lowerdir=readonly,upperdir=readwrite -t overlayfs
echo "Making new squashfs"
mksquashfs merged newfilesystem.squashfs -comp xz

echo "Unmounting merged, casper-rw and old squashfs"
umount merged
umount readwrite
umount readonly

echo "mounting new squashfs and making new manifest"
mount newfilesystem.squashfs readonly -o loop,ro -t squashfs
chroot readonly dpkg-query -W --showformat='${Package} ${Version}\n' > newfilesystem.manifest
printf $(du -sx --block-size=1 readonly | cut -f1) > newfilesystem.size 

echo "unmounting new squashfs and copying back to usb"
umount readonly

cp newfilesystem.squashfs ${usbpath}casper/filesystem.squashfs
cp newfilesystem.size ${usbpath}casper/filesystem.size
cp newfilesystem.manifest ${usbpath}casper/filesystem.manifest

echo "resetting casper-rw"
mkfs -t ext3 ${usbpath}casper-rw

echo "cleaning up"
cd /var/tmp
rm -rf usblive