I mean, server machines usually don't have a display screen or keyboard. So what are the general ways through which system administrators install server side applications or managing the system? Do they always use SSH/Telnet from another computer? Are there any other ways?
closed as off topic by Jeff Atwood♦ Jul 20 '12 at 7:25
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This is a very broad question, and doesn't really match Serverfault's FAQ. But here's an answer anyway.
The main way of connecting to the servers is SSH. Never telnet - you never, ever, do any work on an unencrypted connection!
Most modern enterprise class systems have an ILO or RIB interface which is basically a way to SSH to a tiny program that lets you reboot the server as if you were pressing a power button, and connect to the console as if you were using a monitor and keyboard right at the server.
For installing programs, there are different solutions for different OS'es. For example, Redhat offer a satellite server that has a lot of rpm's, and programs running on the server that will periodically check for updates. (I wouldn't want my servers to update automatically; I want to be sure I know what's happening at all times - but that will depend on your environment.) Solaris and HPUX have similar setups. You can also use something like Puppet or cfengine.
TL;DR: For basic access, SSH is the most common way of connecting to the server. There are other ways of installing programs depending on your OS and how much automatioln you want.