On Tue, 2006-05-30 at 14:33 +0100, Ashok Sharma wrote: > Here is a related question. > When I fork() from a process a parent process with > some id is created together with a child process with > pid same a id of parent and id (of child) is zero. (Please correct me if I am wrong or partially right:) ) fork() system calls return twice from the kernel, once it returns for the parent and in this case fork has a return value as the pid of the child as there is no other way for the parent to get the pid of the child. The second return is for a new child (having different pid ofcourse). Here the return value is 0. It doesn't need the pid of the parent as it can easily get that using getppid() call. So, each process(child and parent) has its own pid and what you are confusing as pid is only the return value. > > Now if from a child I fork() again then what will be > the pid and id of the child (or grand child) now. Both > cannot be zero again and what happens if I fork again > from the grand child? > > Pl. clear my doubt > This, I suppose, stands cleared now.... > Cheers > ashok > > Hope this helps.... Taha > > > > > --- Gopala Krishna <gopalakrishna.n.m@xxxxxxxxx> > wrote: > > > > > > > Fortunately, here comes the proc filesystem ! > > > So, you have the pid of the father process : look > > at the file > > > /proc/'ppid'/status there should be a fild ppid : > > you have the pid of > > > your grand parent. > > > You can do a recursive function to find all the > > ancestors of your > > > process. > > > This solution is quite annoying since you have to > > handle files, but it > > > works. > > > > > > If this solution is not acceptable for you, you > > can look at the pstree > > > source code. > > > > > > I don't know if you wanted to do that in your own > > programm or just > > > wanted some soft to give you the entire tree (like > > pstree). Anyway... : > > > > > > > > In My case, I knew only pid of the first process. I > > want the top down > > approach rather than the bottom up (i.e if I know > > child, I know parent. but, > > my requirement is to find out child and it's grand > > children, If I know the > > parent pid). Currently I am going through pstree > > code. > > > > Thanks and regards, > > Gopal. > > > > > > > > > ___________________________________________________________ > Win tickets to the 2006 FIFA World Cup Germany with Yahoo! Messenger. http://advision.webevents.yahoo.com/fifaworldcup_uk/ > > -- > Kernelnewbies: Help each other learn about the Linux kernel. > Archive: http://mail.nl.linux.org/kernelnewbies/ > FAQ: http://kernelnewbies.org/faq/ > -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
