0

Answer to this would really help me out with the master thesis.

I created custom Ubuntu 18.04 Live CD .iso image that comes preinstalled with certain packages (NodeJS, Chrome, Java, MongoDB). However the installation of the packages was separated into multiple .squashfs files that were all placed in /casper/ folder of the .iso image. Thing that is bothering me is that I don't know what mechanism is Ubuntu LiveCD using when multiple squashfs files are uncompressed and they need to be mounted as a single filesystem. Is AUFS or UnionFS doing this work in the background?

Take a look at the image that shows the content of the casper directory of the .iso image: casper dir

(Note: there are 5 .squashfs files there in the casper dir - filesystem.squashfs, chrome.squashfs, java.squashfs, mongodb.squashfs, nodejs.squashfs). The filesystem.squashfs is the biggest out of these 5, and holds almost all packages, while other 4 .squashfs files contain the difference between the base filesystem.squashfs and a filesystems that have NodeJS/MongoDB/Java/Chrome installed. (This is not critical information for the question, the main point is what does Ubuntu Live CD do with these squashfs files when the system is run, and how are they merged to a single filesystem?)

Note: When I run this live cd .iso image as a VM, I can confirm that nodejs, mongodb, java and chrome are all installed.

Resources I followed but was unable to get the answer: http://aufs.sourceforge.net/aufs2/report/sq/sq.pdf https://wiki.ubuntu.com/LiveCDUnionFS https://wiki.ubuntu.com/KernelTeam/LiveCDUnion https://wiki.ubuntu.com/LiveCDStackedFileSystem

Dajan Bračković
  • 1
  • 1
  • If you could boot the ISO, you should be able to tell from output of `mount` – muru Mar 11 '21 at 05:53
  • Thanks @muru, You can take a look at the output from mount here: https://pastebin.com/7DCMdt59 Here is the important line: /cow on / type overlay (rw,relatime,lowerdir=//nodejs.squashfs://mongodb.squashfs://java.squashfs://filesystem.squashfs://chrome.squashfs,upperdir=/cow/upper,workdir=/cow/work) Does this mean it is overlayFS being used, and not aufs or unionfs? – Dajan Bračković Mar 13 '21 at 19:59

0 Answers0