I had a recent Ubuntu install with customizations that I wanted to be able to put it on a USB, boot into it on another machine and be able to modify its contents by, installing new packages, editing files, etc…

PinguyBuilder to the rescue

So after a number of false starts. I stumbled upon PinguyBuilder. I followed the excellent instructions at maketecheasier, with the slight modification of checking the PinguyBuilder site for the the latest version. I used the backup option to get all the tweaks on home directory, and my none deb packages in. My Ubuntu was a derivative the standard Xubuntu 16.04 distro.

Moving the ISO to the USB

The generated iso file could then be installed usb-creator-gtk, or if are working on windows, Rufus. At this point I could nicely boot using my USB stick. I could not, however, write anything persistently on the USB. If I create some file, and then reboot, it would be gone!

Making the USB persistent

First I need to create casper-rw file that would be identified by boot-loader as space to write on. I was happy with 2GB, so this what I did by adopting the instructions on StackExchange post:

I created an empty 2GB file

dd if=/dev/zero of=casper-rw bs=1M count=2048

You can changed count to whatever size of persistent storage you want. I then had to format that space into something that Linux would be able to read

mkfs.ext4 -F casper-rw

The next step was to change /boot/grub/grub.cfg file on the USB to have the following menu-entry at the beginning.

menuentry "Xubuntu in persistent mode" {
    set gfxpayload=keep
    linux   /casper/vmlinuz  file=/cdrom/preseed/custom.seed boot=casper persistent iso-scan/filename=${iso_path} quiet splash --
    initrd  /casper/initrd.gz
}

Finally, I modified /isolinux/isolinux.cfg to include the extra label

label persistent 
  menu label live - boot the Live System
  kernel /casper/vmlinuz
  append  file=/cdrom/preseed/custom.seed boot=casper persistent initrd=/casper/initrd.gz quiet splash --

et voilà!