ps not listing PIDs (was Unkillable Process?)

[David Densmore <dden@rollanet.org>]

In case anyone is interested, I figured out why I couldn't list the PID
of the app (Wine/Agent) that crashed my X server.  I had logged out of
the original console from which I started X, and it seems that when I
do that, the PIDs of some of the processes associated with X will no
longer display when I use the ps command.

Here is the output from ps before logging out of the original console:

$ ps w a
  PID TTY STAT TIME COMMAND
  100  S1 S    0:00 /usr/sbin/gpm -m /dev/ttyS1 -t mman -l
"a-zA-Z0-9_.:~/\300-\
  116   3 S    0:00 /sbin/getty 38400 tty3 
  117   4 S    0:00 /sbin/getty 38400 tty4 
  118   5 S    0:00 /sbin/getty 38400 tty5 
  119   6 S    0:00 /sbin/getty 38400 tty6 
  192   2 S    0:00 /sbin/getty 38400 tty2 
  218  S0 S    0:00 /usr/sbin/pppd /dev/ttyS0 38400 defaultroute 
  360   1 S    0:00 xterm -geometry 80x24+135+105 -ls 
  361   1 S    0:00 xterm -geometry 80x20-0-0 -ls 
  345   1 S    0:00 -bash 
  351   1 S    0:00 xinit /home/g7/.xinitrc -- -auth /home/g7/.Xauthority 
  359   1 S    0:00 twm 
  362  p0 S    0:00 -bash 
  363  p1 S    0:00 -bash 
  368  p1 R    0:00 ps w a

And here is the output of ps after logging out of the original console:

$ ps w a
  PID TTY STAT TIME COMMAND
  100  S1 S    0:00 /usr/sbin/gpm -m /dev/ttyS1 -t mman -l
"a-zA-Z0-9_.:~/\300-\
  116   3 S    0:00 /sbin/getty 38400 tty3 
  117   4 S    0:00 /sbin/getty 38400 tty4 
  118   5 S    0:00 /sbin/getty 38400 tty5 
  119   6 S    0:00 /sbin/getty 38400 tty6 
  192   2 S    0:00 /sbin/getty 38400 tty2 
  218  S0 S    0:00 /usr/sbin/pppd /dev/ttyS0 38400 defaultroute 
  371   1 S    0:00 /sbin/getty 38400 tty1 
  362  p0 S    0:00 -bash 
  363  p1 S    0:00 -bash 
  372  p1 R    0:00 ps w a

Notice that PIDs 360, 361, 345, 351 and 359 disappeared from the
list (I think 345 was the original console).  But those processes were
still running and I was still able to kill one of my xterms (PID 361)
even though it no longer was displayed by ps.

Is this normal behavior?  Is is a bug?  Is it at all interesting?
Shouldn't PIDs of all running processes be displayed by ps even if
the user who started it logs out of the console from which it was
started?

Just wondering,
David Densmore <dden@rollanet.org>