Hello. I'm only amateur-ish server administrator, never had serious experience with big production servers, but anyway I feel like answering, and if I was asked these questions I'd answer..
1. What are the security requirements of a server?
First there's physical security, only authorized personnel should have access to the server (which should be duly protected from fire, theft, etc...). Then permissions must be properly set, and the admin must be known and responsible and have a good password that he often changes. The OS and software must be kept up-to-date to plug the latest security holes. On windows there usually must be a solid antivirus solution. This is all software security, and there are a bunch of other solutions which can help secure your server. And of course then there must be backup.
2. What are the key responsibilities in a system admin's job description?
Keep the system updated, running smoothly, and basically it should not deteriorate from one month to the other but stay in the same state. He should implement backups and other necessary procedures if they're not already implemented. If they already exist, then he should oversee they are followed. He should of course monitor and troubleshoot problems, fix them, and document them. An SA must document everything in an clear, orderly and searchable fashion - basically usable documentation. SAs are sometimes required to be available on call and be able to login remotely to fix problems.
He might also be required to take part in planning of an upgrade or migration, and of course execution too.
In times of big problems, he must rebuild the system from backups or other recovery options.
3. What are some of the day to day tasks of a system admin?
Basically checks that all is going fine and nothing is out of the ordinary, improves things if needed, otherwise he can be also laying plans for future upgrades, or executing these plans.
4. What is the average monthly salary of a system admin (in Lebanon of course)?
I think a junior SA can start at as low as $900.
Further inspiration:
http://en.wikipedia.org/wiki/System_administrator#Duties_of_a_system_administrator
