hi all,
thought to explain why a zombie cannot be killed.
main()
{
int pid;
pid = fork(); /*the integer pid now holds the return value of
fork, fork returns the child process id in
parent and 0 in the child process */
if(pid == 0) { /*the body of the if-statement is executed */
sleep(1); /* only in the child*/
exit();
}
sleep(30); /*the parent, straight away goes to sleep*/
}
the above program is a very simple one, all ought to understand it.
fork is a system call used to generate child process. so once we call fork,
we get two process, one the parent and the other the child.
|
|
|
|
fork()
/ \
/ \
/ \
/ \
parent child
fork returns twice, once in parent and once in child. In the parent fork
returns
the process id(PID) of the child, and in the child it returns 0.
so the body of the if-statement is executed in the child process only the child
process sleeps for one second and then exits ie terminates. the parent process
goes on to sleep for thirty more seconds. please note that the child process
was made to sleep for one second to make sure that the parent is sleeping when
the child exit()'s.
and then by definition of a zombie process, the child should have become a
zombie process
because its exit status is not known by the parent, because the 'irresponsible'
parent was
sleeping when its child died.
the below few lines are the last lines of the output of 'ps -l a' command.
100 S 0 412 408 0 75 0 - 554 11d2b8 pts/1 0:00
/bin/bash
000 S 0 417 261 0 72 0 - 309 12228a tty1 0:00
./a.out
044 Z 0 418 417 0 72 0 - 0 11ce8a tty1 0:00
[a.out <defunct>]
000 R 0 420 412 0 77 0 - 669 - pts/1
0:00 ps -l a
and can we see that the parent with pid number 417 is sleeping and the child
with pid 418 is now a defunct process with status shown as Z, meaning Zombie
process( make sure you switch terminal and give command 'ps -l a' before 30
thirty seconds to view this behaviour).
understand why trying to kill a Zombie process just wont work. simply because
its allready dead.
once the parent wakes up after 30 seconds it gets the status of the child
process and the zombie child vanishes( 'ps -a l' after the parent has
terminated to see this).
another way to get rid of the zombie is to kill the parent process, in this
case 'kill -9 417' will kill the parent and take out the zombie as well, 'ps -a
l' after killing the parent to see that the zombie has vanished.
please reply to the post if i have made a mistake in grasping the concept
and/or if things are out of context and/or if there is something more to be
explained. also please explain if Zombies can be 'eliminated' in any other
way, i remember to have seen code to eliminate
all the zombie processes. is this possible.
justin
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From [EMAIL PROTECTED] Sat Dec 4 12:57:33 2004
From: [EMAIL PROTECTED] (justin joseph)
Date: Sat Dec 4 12:57:37 2004
Subject: [Mailinglist] please suggest an internel modem.
Message-ID: <[EMAIL PROTECTED]>
hi all,
lightening has damaged my internel modem(dfm 560is). can some one please
suggest an internal modem which works with atleast 2.4.18. the damaged one
worked only with 2.4.4
every time the module for the modem is being loaded the booting process stops,
no use restarting too. i could only manage to boot up after removing the
modem. this is how i decided that the modem is damaged.
please do not suggest an externel modem, cannot afford one.
justin
---------------------------------
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From [EMAIL PROTECTED] Sat Dec 4 13:13:17 2004
From: [EMAIL PROTECTED] (Rajesh)
Date: Sat Dec 4 13:13:23 2004
Subject: [Mailinglist] please suggest an internel modem.
In-Reply-To: <[EMAIL PROTECTED]>
Message-ID: <[EMAIL PROTECTED]>
--- justin joseph <[EMAIL PROTECTED]> wrote:
> hi all,
>
> lightening has damaged my internel modem(dfm 560is).
> can some one please suggest an internal modem which
> works with atleast 2.4.18. the damaged one worked
> only with 2.4.4
>
> every time the module for the modem is being loaded
> the booting process stops, no use restarting too. i
> could only manage to boot up after removing the
> modem. this is how i decided that the modem is
> damaged.
>
> please do not suggest an externel modem, cannot
> afford one.
>
> justin
>
>
please buy a kobian modem with netodragon chip
and linux download driver from www.netodragon.com
for more details contact after getting the device and
driver
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