how does live (CD version) of Ubuntu work ?

[wpshooter]

I recently ordered some copies of the live CD version of Ubuntu. Unfortunately, I have not received yet.

But when I do, if this is ran directly off of the CD (and not installed to system hard drive), when various writes, working files, etc. are created by the operating system where is all this information written to ? Is this type of info written back to the CD (and if so, I would assume that the CD has to be RW capable) or is all of this temporary info written to memory and if so, what would be the lowest amount of memory that this operating system could perform in ?

Thanks.

 

[Noema]

Good question; I'd like to know too, as I've been toying around with the Ubuntu live CD as of late and rather liking it. In fact, I'd go Lynux if it weren't for my ATI card.

I assume that it either creates a temporary directory in which it caches some stuff, or it creates some sort of RAM drive where the info is stored and wiped upon reboot, but that's just mere speculation.

 

[kamper]

Live cd's usually use ram drives, so all your changes would simply disappear the next time you boot. Frequently though, you can mount the filesystems that are already on your hard drive and write to them (permanently...). I've also heard of some that work together with a usb key but I'm not sure of the details. I think some work with cds, but it's not like a normal file system. It might flush all your changes to one file on the cd and reload those next time, then the next time you shut down, it would have to create a whole new file (obviously not very scalable).

 

[wpshooter]

Originally posted by: Noema
Good question; I'd like to know too, as I've been toying around with the Ubuntu live CD as of late and rather liking it. In fact, I'd go Lynux if it weren't for my ATI card.

I assume that it either creates a temporary directory in which it caches some stuff, or it creates some sort of RAM drive where the info is stored and wiped upon reboot, but that's just mere speculation.

Alas, what is the problem with ATI, since that is what I am using in all of my computer ?

 

[Noema]

Originally posted by: wpshooter

Originally posted by: Noema
Good question; I'd like to know too, as I've been toying around with the Ubuntu live CD as of late and rather liking it. In fact, I'd go Lynux if it weren't for my ATI card.

I assume that it either creates a temporary directory in which it caches some stuff, or it creates some sort of RAM drive where the info is stored and wiped upon reboot, but that's just mere speculation.

Alas, what is the problem with ATI, since that is what I am using in all of my computer ?

Well, pretty much the only reason I stick with WinXP is because I play a lot of Wolrd of Warcraft.

WoW is very playable in Lynux with WINE (some of my guildmates play it that way, and report even better framerates than in Windows in some cases), but ATI Lynux drivers aren't adequate enough and configuring the OpenGL to work properly has been a nightmare, at least in my case. Nvidia drivers are much better, it seems.

This of course is only an issue if you are a gamer.

 

[drag]

On the 'live' cd it will contain a few compressed filesystems in the form of a single file. These are called loopback file systems. You mount the loopback file systems and the data is read into memory as you access it...

Also it helps that the nature of Linux is to have strong barriers to users having access outside their own home directories and /tmp directories. This has a side effect that allmost all the programs you use can be used on a read only file system with only needed write access to /tmp and /home.. which works out great for a cdrom system.

Not all loopback file systems have to be read-only, but in this case with the cdrom it has to be.

Also there are other tricks they can do. Like setup a file system, then mount another system ontop of that one so that you can read and access the 'bottom' system, but when you make new files it gets added to the new one. I forget what that is called, though.

But mainly... The main / (root) file system is mounted read-only and is a loopback system on the cd.

Other ones include /home/ and /tmp and those would be mounted in tmpfs inside ram as a 'ramdisk', then others like /dev/ and /proc/ and /dev/ are "virtual" file systems that are naturally mounted in ram even if you just using a normal linux install.

Loopback file systems are cool, and it's also the easiest way to setup a encrypted fs in Linux.

For instance take your ISO image file. It's a cdrom image, but it can be mounted as loopback if you wanted.

So if you have a iso image file and you want to try to mount it loopback you go like this:
(say it's called randumb.iso)

mkdir temporary
sudo mount -t iso9660 -o loop,ro randumb.iso temporary/

The mount is the command to mount file systems. the -t iso9660 tells mount that it's a ISO 9660 file system, which is what data cdroms are. This option isn't nessicary most of the time because mount will autodetect the file system, but the autodetect doesn't always work. The -o loop,ro tells it to mount it as a 'loopback' file sysetm and that it's read-only.

So that way when you download iso image you can mount it loopback to get access to it without having to burn a actual cdrom. Also it's good for testing after you use dd to make a iso image or you want to play games that require having the cdrom present (although sometimes game makers will intentially break the ability to make iso images by doing weird things)