How do I find all child processes in Unix?

First off, I have to say that it sounds like the application isn't too well written if you're seeing this sort of process conflict, but that's the pragmatic reality of life on servers, I think.

Fortunately, the solution is fairly straightforward.

First off, you can find the process ID (PID) of the parent process by using a sequence of ps -aux | grep pattern. If your life is going to be easy, there'll always only be one match, but if there are also child processes, it's a bit more tricky.

In general, modern versions of ps let you specify exactly what fields you want to have output with the '-o' flag, so here's how I'd approach that for a process called "httpsd":

$ $ ps -o user,pid,ppid,command -ax | grep httpsd
root   47248     1 /usr/local/apache/bin/httpsd
www    47249 47248 /usr/local/apache/bin/httpsd
www    47250 47248 /usr/local/apache/bin/httpsd
www    47251 47248 /usr/local/apache/bin/httpsd
www    47252 47248 /usr/local/apache/bin/httpsd
www    47253 47248 /usr/local/apache/bin/httpsd
www    92713 47248 /usr/local/apache/bin/httpsd

In this output you can see that the first column shows the userID, the second shows the PID, and the third the PPID. Notice that the parent process not only has PPID of 1, but also is the only one running as root. This makes it easy to mask that one out and identify all the processes that are spawned by the "httpsd" program:

ps -o user,pid,ppid,command -ax | grep httpd | grep -v root

But that's not exactly what you're asking. Instead, you're asking me how to identify processes based on their PPID. To do that, let's drop the PID of the parent into a variable first:

pid=$(ps -o user,pid,ppid,command -ax | grep httpd | \
  grep root | awk '{print $2}')

Now I have a variable "pid" that has the process ID of the parent application. To find all the child apps, I just search for those that have that particular PID as their PPID.

That's actually just a slightly more complex awk script needed, as demonstrated in this snippet:

for child in $(ps -o pid,ppid -ax | \
   awk "{ if ( \$2 == $pid ) { print \$1 }}")
do
  echo "Killing child process $child because ppid = $pid"
  kill $child
done

That should do what you seek!