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Top Forums UNIX for Dummies Questions & Answers Processes, Services, Daemon's and Subsystems Post 41865 by davidg on Thursday 16th of October 2003 05:48:30 AM
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
 

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PTHREAD_ATFORK(3)					     Library Functions Manual						 PTHREAD_ATFORK(3)

NAME
pthread_atfork - register handlers to be called at fork(2) time SYNOPSIS
#include <pthread.h> int pthread_atfork(void (*prepare)(void), void (*parent)(void), void (*child)(void)); DESCRIPTION
pthread_atfork registers handler functions to be called just before and just after a new process is created with fork(2). The prepare han- dler will be called from the parent process, just before the new process is created. The parent handler will be called from the parent process, just before fork(2) returns. The child handler will be called from the child process, just before fork(2) returns. One or several of the three handlers prepare, parent and child can be given as NULL, meaning that no handler needs to be called at the cor- responding point. pthread_atfork can be called several times to install several sets of handlers. At fork(2) time, the prepare handlers are called in LIFO order (last added with pthread_atfork, first called before fork), while the parent and child handlers are called in FIFO order (first added, first called). To understand the purpose of pthread_atfork, recall that fork(2) duplicates the whole memory space, including mutexes in their current locking state, but only the calling thread: other threads are not running in the child process. The mutexes are not usable after the fork and must be initialized with pthread_mutex_init in the child process. This is a limitation of the current implementation and might or might not be present in future versions. RETURN VALUE
pthread_atfork returns 0 on success and a non-zero error code on error. ERRORS
ENOMEM insufficient memory available to register the handlers. AUTHOR
Xavier Leroy <Xavier.Leroy@inria.fr> SEE ALSO
fork(2), pthread_mutex_lock(3), pthread_mutex_unlock(3). LinuxThreads PTHREAD_ATFORK(3)
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