so what should i use my extra 4096 for?
im running ubuntu 10 on a 512 with 256 swap. should i increase swap or increase root?
if i instead create a second image will i need a second ip address?

Main disk space. There is no need to increase swap for the majority of users since if you need more memory, it's best to just go with a RAM upgrade. If you have two images of OSes, only one will be able to be run at a time - you pay for one linode and get one instance of an OS. Sure, you can have two disks then boot up a different one, but it would mean your original disk and OS being idle.

yeah i thought that would be the case.

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linode 512, ubu 10, apache2, php, mysql