Re: Kill Process ERROR !!!

On Wed, 9 Jul 2003, Terry Hampton wrote:

> Andrew Sullivan wrote:
> > On Wed, Jul 09, 2003 at 09:52:38AM +0000, aris wendy wrote:
> >
> >>I want to kill process no 582, I use kill -9 582 but all user become
> >>disconnect  look at below
> >
> >
> > Try kill -2.
> >
>
>         The   " kill -2 "  is much better advice.
>
>         Might I suggest to all -   AVOID   the " classic "  kill -9  !
>         Never use it,  unless nothing else works.  It's curious why
>         " kill -9 " is such a part of " common "  UNIX practice.
>
>         Yes it works, but it's messy and often leads to problems as
>         Andrew experienced.       The "9" signal is too brute force,
>         and should only be used as a LAST resort.
>
>         Your first command to kill a process is simple:    kill  <pid>
>
>         Notice - NO signal value.  By default UNIX sends a signal 15
>         with the kill command.      Signal 15 is the default because
>         it is the normal termination signal. ( I don't have a manual in
>         handy to give you the exact name of the signal ).  Signal 15
>         should ALWAYS be used first since it tells the process to
>         terminate as if the process was terminating on its own.  This
>         means, the process will more likely clean up after itself,
>         regarding file descriptors, child processes, etc.

What amazes me is how many people don't try 'kill pid' first.

>         Speaking of child processes, ALWAYS kill any child processe
>         first - and more specifically from high to low PID value.  Basically,
>         the higher the PID value, the newer or younger the child.  Why
>         kill child processes first ?  -   UNIX processes are very signal
>         driven.  The parent of any  processes looks for signals from its
>         children, and acts accordingly.    Processes always have a parent.
>         Child processes that are orphaned,   are sometimes " adopted " by
>         another process - and that is always process 1           Usually,
>         this is the story behind " zombies " - those processes you can't
>         kill or will go away.  Next time you see a <zombie>, notice its
>         parent PID is 1.

Please note that this is not necessarily true.  If my server has been up a
while and I stop/restart the postmaster, it may have a fairly high id
number and it is quite possible that in x number of days time, the
children will be created with a wrapped pid which is lower than the
postmasters.  Just look for the - switches that make it obvious.  In fact,
this IS currently the case right now on my server:

13081 ?        S      2:30 /usr/local/pgsql/bin/postmaster
13082 ?        S      0:19 postgres: stats buffer process
13083 ?        S      0:28 postgres: stats collector process
 5600 ?        S      0:00 postgres: marlowe phone [local] idle

In this case 13081 is my postmaster.

Notice that kill -9 to any postgresql backend results in all backend
connections flushing their buffers.  kill -9 to the postmaster results in
a dirty shutdown and the database server has to go through the WAL and
clean things up.  It's not the same as hitting the Big Red Switch, but
it's close.