Daemons and modules ?

[Johnthom]

Hi everyone,

By setting up many services in my system, I found out there are different kinds of server operating. For example, telnet, ftp, dns ... work in form of daemons, and some services work in form of modules like Iptable, pchains... So I wonder what is the differnce between two these forms, why Iptable/ipchains doesn't work as daemon but module form. Please give me your explanation and a couple of examples for services operating in form of modules.

Thanks so much.

John Thom.

 

[ifincham]

Hi,

Packet filtering is logically part of the operating system and, as such, it needs to either be built-in to the kernel or loaded as a kernel module. Iptables / ipchains need to integrate themselves into the core networking functionality of the kernel and could be roughly compared to something like the code that effects rwx file permissions. You would not want the integrity of this code undermined in any way.

Daemons, by contrast, are effectively user space server applications that are not part of the operating system as such. A daemon could be compared to an application program that, once loaded, does not terminate but listens on sockets for client connections and takes appropriate action. For example, a web server like apache or ftp server, etc. All those kind of applications reside at the top of the OSI model (layer 7) whereas IP is much lower down - layer 3. The fact that some daemons run as root is more to do with needing to bind to privileged ports, file permissions, etc. rather than because they are anything to do with the operating system itself.

Hope this helps