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Processes, Services, Daemon's and Subsystems


 
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Top Forums UNIX for Dummies Questions & Answers Processes, Services, Daemon's and Subsystems
# 1  
Old 10-14-2003
Question Processes, Services, Daemon's and Subsystems

I'm just wondering what the differences/relationships there are between processes, services, daemons and subsystems?
I keep coming across these terms but I can't find clear definitions/explanations of these terms.

Smilie
# 2  
Old 10-16-2003
Good Question!

To understand processes you have to pick up a Operating System book.

In general terms, a process is a job or time-shared program. Processes can also have subprocesses and so on.

A daemon is a server process that waits for communication.

Handeling processes is another story.

Smilie
# 3  
Old 10-16-2003
You forget one "port-number" Smilie

A service, is a service a server can offer.

F.e. ftp

ftp is a service taken in /etc/services,
it has a specific port onwhere it should communicate with.
Therefor a daemon (inetd) is started that keeps track of any incomming or outgoung requests on that port.
This daemon runs as a process as it's claiming memory/cpu-time/IO-resources.

Subsystem is quiet unknown with me, Maybe you mean the child of a Parent process. Sometimes a process can fork and create a child to have a job done for him. We call this the parents child.
f.e. :
running a shell gives you a process (ps -ef | grep sh | grep -v grep). Now performing an "bdf ." will fork your shell into a process that will find out the diskusage for your current directory. when it is finished the child automaticly dies (stops) and goes back to it's parent.

Well, enough fast-course Unix Smilie
Anymore questions, just let us know.

Regs David
# 4  
Old 10-16-2003
A subsystem is a piece of a system. The memory management unit and floating point coprocessor could be called subsystems of a cpu.

{lp, lpstat, lpsched, accept, reject, enable, disable } could be called the printer spooling subsystem.
 

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