topic Re: WCHAN field in ps in Operating System - HP-UX

WCHAN field in ps

Romeo_Lou — Thu, 15 Apr 2004 04:42:50 GMT

Dear,
How can I know the process is waiting for what/or blocked from somebody?
WCHAN field in ps?

tks a lot

Re: WCHAN field in ps

Bharat Katkar — Thu, 15 Apr 2004 05:32:57 GMT

WCHAN indicates the event for which process is wating, if hypen is placed in that field the process is not waiting or sleeping.

I think that should help U.

Re: WCHAN field in ps

Kent Ostby — Thu, 15 Apr 2004 05:54:06 GMT

WCHAN stands for "wait channel".

The value listed by the ps command shows a hexidecimal address of the resource that you are waiting or sleeping on.

Best regards,

Kent M. Ostby

Re: WCHAN field in ps

Navin Bhat_2 — Fri, 16 Apr 2004 11:01:27 GMT

If your goal is to find out what the process is blocked on/ waited on then try using glance as a first step, go into the process details and you could see what it is blocked on or the wait's on.

You could use wchan also to get the function it was waiting on using adb. Again know what you are going for, there could be multiple threads/process waiting on the same wchan. If you need further assistance you could open a support call into HP.

Re: WCHAN field in ps

Mike Stroyan — Mon, 19 Apr 2004 15:47:36 GMT

The WCHAN value is not a function address. It is actually the address that was passed into a call to sleep() in the kernel. It should later be used in a call to wakeup().

The WCHAN address is sometimes a global variable with a name that you could match to some particular driver or system call. At other times it is an allocated address that has no particular meaning outside of the kernel code that is making those calls.

You can get a look at what symbol a WCHAN value maps to using adb to print it as a symbolic address. Here is a little script that looks at the WCHAN values of all the processes on the system.

for a in $(UNIX95=1 /usr/bin/ps -e -o wchan | sort | uniq)
do
print "0x$a?a"
done | adb /stand/vmunix