04-25-2002
what are parent and child processes all about?
I don't follow what these are...
this is what my text says...
"When a process is started, a duplicate of that process is created. This new process is called the child and the process that created it is called the parent. The child process then replaces the copy for the code the parent process created with the code the child process is supposted to execute."
The last sentance confuses me the most. Actually the entire thing confsues me. Why is a child process started anyways? Why does the parent process spawn a child process in the first place? And what's all this code copy stuff all about?
The next paragraph states...
"While the command is executing, the shell waits until the child process has completed. After is completes, the parent process terminates the child process, and a prompt is displated, ready for a new command"
Why does this happen? I guess it goes back to my confusion about why the child process is created in the first place.
10 More Discussions You Might Find Interesting
1. Filesystems, Disks and Memory
:(
Since I'm fairly new to the scene and don't have much experience in shell programming, I decided to check out the net for a useful script or two.
What I'm looking for is a script that would let me enter a PID and then show the process tree associated with it.
So it would display the (grand-)... (2 Replies)
Discussion started by: velde046
2 Replies
2. UNIX for Dummies Questions & Answers
Hello all,
I have gone through the search and looked at posting about idle users and killing processes. Here is my question I would like to kill an idle user ( which I can do) but how can I asure that all of his process is also killed whit out tracing his inital start PID. I have tried this on a... (4 Replies)
Discussion started by: larry
4 Replies
3. Shell Programming and Scripting
Hello.
I have a global function name func1() that I am sourcing in from script A. I call the function from script B. Is there a way to find out which script called func1() dynamically so that the func1() can report it in the event there are errors?
Thanks (2 Replies)
Discussion started by: yoi2hot4ya
2 Replies
4. UNIX for Advanced & Expert Users
Hi
I am trying to see if there are some options in ps command or if there is a shell script which basically shows you all the processes spawned by a parent process , then all the processes of its child processes and so on down the hierarchy may be like a tree structure. It might be a generic... (6 Replies)
Discussion started by: clifford
6 Replies
5. UNIX for Dummies Questions & Answers
Consider this simple command line
bash -c 'echo $$ ; sleep 10000'This will print the newly created bash PID and sleep for a long time.
If I go to another terminal and do something like
ps -flax | grep leepI'll see something like
501 92418 91910 0 0:00.00 ttys000 0:00.00 bash -c echo $$... (5 Replies)
Discussion started by: teras
5 Replies
6. Shell Programming and Scripting
Hello,
I am trying to create a pipe that will direct stdout to in side of the pipe, and stdin to the out side of the pipe - I created two child processes to handle this. However, my pipe doesn't seem to be working correctly. Did I use execv() correctly? Command1 and command2 represent the two... (3 Replies)
Discussion started by: jre247
3 Replies
7. Homework & Coursework Questions
1. The problem statement, all variables and given/known data:
I need to make an program that in a loop creates one parent and five children with fork(). The problem i'm trying to solve is how to delete the parent and child of the childīs process.
2. Relevant commands, code, scripts,... (0 Replies)
Discussion started by: WhiteFace
0 Replies
8. Programming
Hi friends,
I have a small question regarding unix system call fork, I hope you will solve my problem. Here is the small program
$ cat fork1.c
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
int main()
{
int pid;
int x = 0;
x = x + 1;
pid = fork();
if(pid < 0)
{... (2 Replies)
Discussion started by: gabam
2 Replies
9. Shell Programming and Scripting
Hi everyone
i am very new to linux , working on bash shell.
I am trying to solve the given problem
1. Create a process and then create children using fork
2. Check the Status of the application for successful running.
3. Kill all the process(threads) except parent and first child... (2 Replies)
Discussion started by: vizz_k
2 Replies
10. Shell Programming and Scripting
I am trying to kill PIDs that are tied to a KSH "load_sqlplus" and I am using the below code
LIST_PID=`ps -ef | grep -i "load_sqlplus" | grep -v grep | awk '{print $2}'`
if ; then
echo "Processes killed" "PID : " $LIST_PID
kill -9 $LIST_PID
else
echo "Nothing to Kill"
fi... (4 Replies)
Discussion started by: venky338
4 Replies
FORK(2) BSD System Calls Manual FORK(2)
NAME
fork -- create a new process
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <unistd.h>
pid_t
fork(void);
DESCRIPTION
fork() causes creation of a new process. The new process (child process) is an exact copy of the calling process (parent process) except for
the following:
o The child process has a unique process ID.
o The child process has a different parent process ID (i.e., the process ID of the parent process).
o The child process has its own copy of the parent's descriptors. These descriptors reference the same underlying objects, so that,
for instance, file pointers in file objects are shared between the child and the parent, so that an lseek(2) on a descriptor in the
child process can affect a subsequent read(2) or write(2) by the parent. This descriptor copying is also used by the shell to
establish standard input and output for newly created processes as well as to set up pipes.
o The child process' resource utilizations are set to 0; see setrlimit(2).
In general, the child process should call _exit(2) rather than exit(3). Otherwise, any stdio buffers that exist both in the parent and child
will be flushed twice. Similarly, _exit(2) should be used to prevent atexit(3) routines from being called twice (once in the parent and once
in the child).
In case of a threaded program, only the thread calling fork() is still running in the child processes.
Child processes of a threaded program have additional restrictions, a child must only call functions that are async-signal-safe. Very few
functions are asynchronously safe and applications should make sure they call exec(3) as soon as possible.
RETURN VALUES
Upon successful completion, fork() returns a value of 0 to the child process and returns the process ID of the child process to the parent
process. Otherwise, a value of -1 is returned to the parent process, no child process is created, and the global variable errno is set to
indicate the error.
ERRORS
fork() will fail and no child process will be created if:
[EAGAIN] The system-imposed limit on the total number of processes under execution would be exceeded. This limit is configuration-depen-
dent.
[EAGAIN] The limit RLIMIT_NPROC on the total number of processes under execution by this user id would be exceeded.
[ENOMEM] There is insufficient swap space for the new process.
SEE ALSO
execve(2), setrlimit(2), vfork(2), wait(2), pthread_atfork(3)
STANDARDS
The fork() function conforms to ISO/IEC 9945-1:1990 (``POSIX.1'').
HISTORY
A fork() system call appeared in Version 6 AT&T UNIX.
BSD
June 10, 2004 BSD