On Sat, May 24, 2008 at 11:31 PM, Peter Teoh <htmldeveloper@xxxxxxxxx> wrote: > Sent on behalf of William Case: > > From: William Case <billlinux@xxxxxxxxxx> > Date: Sat, May 24, 2008 at 11:26 PM > Subject: fork and exec > > Hi; > > I have a fundamental question about why Linux/Unix uses the parent and > child modal to start and run new processes. > > I am having trouble making my question understood. I tried to get an > explanation from members of my local LUG who are usually quite > responsive and helpful. My question was met with some defensiveness as > if I was challenging the basic way that *nixes do things. I couldn't > seem to get past answers that told me how fork() and exec() work to why > things are done that way. So ... > > I will try my question here: > > Quoting from http://en.wikipedia.org/wiki/Fork_%28operating_system%29 > > "Under Unix and Unix-like operating systems, the parent and the child > operations are selected by examining the return value of the fork() > system call. ...", and, > > "The fork operation creates a separate address space for the child. The > child process has an exact copy of all the memory segments of the parent > process ... ", and, > > "More generally, forking is also performed by the shell each time a user > issues a command. A child process is created by forking the shell, and > the child process is overlaid, once again by exec, with the code > associated with the program to be executed." > > I understand the mechanics of how this works. Several manuals, texts > and Wikipedia give very clear examples. > > To further quote that section of Wikipedia: > > "Forking is an important part of Unix, critical to the support of its > design philosophy, which encourages the development of filters. In Unix, > a filter is a small program that reads its input from stdin, and writes > its output to stdout." > > My question is: Why did the original designers of Multics/Unix choose > to use the forking modal to start a new processes? Do not other OSs use > other modals? What problem(s) did the fork overcome? Couldn't a system > have been designed that just (in some way) starts each process raw? can u elaborate what is meant by "RAW"?? I like new ideas....please elaborate....things necessarily have to be different all the time.....that's how Windows can survive in business.... > Intuitively, copying a process then overwriting it seems wasteful or at > least inelegant, so why is it needed? How does a parent-to-child > process enhance its (*nix's) design philosophy? > > Since forking is at the very core of the kernel, I would like to > understand intellectually why the fork process is necessary? > > I am not being argumentative, or trolling, or proposing something > different or better. Although relatively new to kernel programming and > 'C' I am not a complete newbie. I would just like to see in my > minds-eye what is going on and *why*. > > -- > Regards Bill > -- Regards, Peter Teoh -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
