Why doesn't kill work?

[David Liguori]

Robert Locke wrote:
> On Thu, 2005-01-27 at 21:04 -0500, David Liguori wrote:
> 
>>In another thread a user having problems with yum killed it.  I am 
>>curious how he accomplished that.  When I run yum (or any other command, 
>>for that matter), it stalls, and I stop it with ctrl-z, the following 
>>happens:
>>
> 
> 
> First question, why are you stopping it with Ctrl-Z??  Ctrl-Z puts it to
> sleep into the background.  Why not use Ctrl-C which is the intended
> approach?
> 
> 
>>[1]+  Stopped                 yum update
>>[root at tabby ~]# ps
>>   PID TTY          TIME CMD
>>  6179 pts/0    00:00:00 su
>>  6182 pts/0    00:00:00 bash
>>  6214 pts/0    00:00:21 yum
>>  6220 pts/0    00:00:00 ps
>>[root at tabby ~]# kill 6214
>>[root at tabby ~]# ps
>>   PID TTY          TIME CMD
>>  6179 pts/0    00:00:00 su
>>  6182 pts/0    00:00:00 bash
>>  6214 pts/0    00:00:21 yum ##still running!
>>  6221 pts/0    00:00:00 ps
>>[root at tabby ~]# exit
>>logout
>>There are stopped jobs. ##still running!
>>[root at tabby ~]#
> 
> 
> This is working as intended.  You are using the kill command correctly
> by sending the default signal first (15), the problem is that you put
> the process to sleep earlier with the Ctrl-Z so it cannot "process" the
> TERM (15) signal that you have sent.  You could at this point bring the
> process to the foreground waking it up by using the "fg" command, or you
> could awaken it in the background using the "bg" command.  Once the
> process is awake, it will process the signal and go away.
> 
> BTW, I would not recommend, as many people are wont to do, and jump onto
> the KILL (9) signal.  If your process is still writing things to disk
> (asleep or awake), this signal pulls the proverbial rug out from
> underneath and you run the risk of ending up with corrupted data
> depending on the process.  Use the KILL (9) signal only as a last
> resort.
> 
> I think most books now say this is the proper order:
> 
> Ctrl-C
> kill -15
> kill -9
> 
> HTH,
> 
> --Rob
> 
Thanks for all the help on this.

 --
Dave