UNIX for Dummies Questions & Answers

I am trying to write a simple shell script to find a hanging pid and kill it.Any idea how to find a hanging pid??

What exactly do you mean by "hanging" pid?

$! = PID of last background process
$$ = PID of current process (self)

we have a content managemnet tool meant for creating templates.sometimes the app is up&running but when we try to create a template we get an hourglass,at that time is there anyway to tell it's pid is hanging on the unix console??
Moreover,when the app doesn't respond we can't just stop it,we have to use kill -9 to kill it's pids.I hope this will explain what I meant by a hanging pid!!

Its really difficult to say if a Process is hanging, only thing we can do is keep looking at what the process has been doing with the ps. If it is Idle for more than some time, assume it is hanging! This is not a solution, but should help you a little.

Hey!! Ravi,
thats an interesting problem. I havent ever heard of any method to find a "Hanging PID" as such. All that I could have done in this case is send harmless signals to the process. A "hanging process" in the foreground wont respond to any signal other than the "Kill -9". This may be used one of the methods to find a "hanging PID" if it doesnt respond to these signals for a "user defined amount" of time depending upon the specific working environment.

This is not a full proof method, but can be considered as one of teh possibilities.

And I dont really think that finding whether process is "idle" can be a right crieteria. Bcoz, "Hanging PID" is not an idle process. It is still running.. besides there may be many process like a telnet session which is not "hanging" but still can be inactive for hours together.

Any process will Terminate if it does not catch a SIGNAL passed to it, SIGKILL (also SIGSTOP) being a signal which can not be caught. So, where's the room for this "hangin process" not to respond if it has not been written to take care of these signals? Which is like terminating the process with 'kill -9' itself! What if the process has been written to ignore any of the passed signals, again the state of the process is not going to change! What if the process has been written to perform some other task on receipt of any of these signals, the program might deviate from it's original task!

And yes, what are those "harmless signals"?

typically when I see a hung PID on my boxes, I can tell that it is hung usually because the run time is very high (somewhat subjective) and the CPU usage is usually very high as well.

We call those "runaway processes". At my work, we use BMC Patrol as a monitoring tool. If the process runs for longer than X minutes, it is flagged and I get a page or email depending on how I have it set to notify me. Also, on HPUX, I have the "top" command and "glance" that help me diagnose system usage.

You can ps -fu user, if you know the user who started the Process and capture the PID if the time and cpu useage is high.