A server daemon is a software package running on a server computer which allows access & communication from a network,
or the internet, to the server itself. For example when you surf around on the internet you are basically asking a web server
(or put another way, a computer running a web server daemon, like apache) to send you the index.htm file that is stored at the
address http://www.highasakite.net or http://62.226.81.152 for display through your browser, a typical client-server relationship.
For each different type of service & communication there is a server daemon controlling it. A server computer may have
many server daemons , to many hundred, running on it. Each daemon service is assigned a particular channel, a so called port,
to which it accepts communication from the outside world. Take a http daemon like Apache for example it listens on port 80, by
default, of the server for any incoming communication. When a visitor lands on the website a connection is built up between the
two computers & this connection is maintained until the visitor no longer sends any requests for pages & files, i.e. he/she
leaves the site. As soon as this peer-peer connection is established Apache starts another daemon & continues listening on port
80 for the next incoming communication. In this way a daemon can handle many requests simultaneously & still be able to listen for more.
For each type of service there is a server daemon available to carry out that task, for example POP3 & SMTP daemons for sending
& receiving emails. When you send an email from your computer at home it is sent in a predefined form to your provider
(like www.gmx.net, www.hotmail.com) where a SMTP server daemon,
most likely Sendmail, is waiting to take over the further mailing to its final destination. The POP daemon works in the same way.
On my server I use a small programme called fetchmail to collect all my emails from all my accounts & then save them on the my
server, where a POP daemon listens & then delivers the mails within my home network upon request.
In the directory /sbin/init.d are all the server daemons binaries that are installed on your Suse system.
All of these daemons can be stopped, started, or rebooted by typing...
/sbin/init.d/apache stop will stop the http daemon Apache for example. By typing netstat –an you get a list of all the
current connections from all the daemons & to which port they are connected.
