Well...a shell account is helpful to learn security only if you are trying to set up your own ISP or web server and want to act as a system administrator. Do you want to learn to work with a shell account / linux just on academic purpose, or you have anything specific on mind?
If you just want to make your web site secure, then you can leave the shell account part out of the syllabus. As you will really not have much control on the web server. The system administrator of the host you choose will take care of that. And he won't relinquish root control over the web server.
Now a days, a shell account on a remote server almost serves no function at all. Because most of the commands and daemons are being disabled by the sys-admin for fear of abuse. In early days anonymous shell accounts had been widely abused and misused by a number of crackers. Most such shell accounts these days won't even let you run a finger query!
But yes, as DK says, if you get a linux machine on a cable connection, you do get a shell account and can use all the standard linux shell commands, depending on the linux distribution you choose. Then you can install and run an apache server, use it to test and debug your web site and even publish your web site for the internet from your home! A cable connection gives a very decent and enough upload speed IF there are not too many people sharing the same network in your neighborhood.
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