How do Live distro's essentially work?

lumix · 11-10-2008, 08:16 AM

All Live CD's that I've used allow you to install apps, create documents, etc, but none--of course--would retain any of these changes after rebooting. So how is this done? Some kind of temporary filesystem is created: is it in ram only? or is it in a reserved disk space (that doesn't seem right because I believe you can run these with no HDD). How is this temporary filesystem created/mounted/, and what is the, er, image(?) that is copied into it?

pixellany · 11-10-2008, 08:36 AM

Basically, the directory tree is created in RAM---I assume the mechanism is similar to a "RAMdisk". I think some things get pulled off the CD only as needed. (Watch for the CD running when you do different things.)

Installing something or creating a file just puts the data into the RAMdisk, which disappears at shutdown.

LiveCD distros are not intended for regular use---only for evaluation.

Google will find much more---and better--info.

brianmcgee · 11-10-2008, 09:20 AM

UnionFS [1] is used to merge a readonly device with a writeable ramdisk.

Some Live-CDs are actually used only from CD. For example security CDs so that no trace is left on your computer after you turn it off.

[1] http://en.wikipedia.org/wiki/UnionFS

salasi · 11-10-2008, 01:11 PM

There isn't necessarily a single answer to this.

UnionFS is probably considered the 'more modern' way to do this, but you'll probably find some live CDs that don't do this because they are old (or the deep voodoo in their internals is old, even if its a new release) and some other live CDs go for the 'start by copying everything to a partition mounted from ram' approach (which works if there is enough ram and only gets used selectively if there isn't).

lumix · 11-12-2008, 09:15 PM

unionFS...interesting. I'll check that link for some more info. Thanks.