Re: Process ID's

[ndt1001@chu.cam.ac.uk (Neil Turton)]

Marcelo Magallon <mmagallo@efis.ucr.ac.cr> wrote:
> I've been seeing this really often since we installed Debian. Is this normal?
> 
> Here's the output of "ps x"
> 
>   PID TTY STAT  TIME COMMAND
> 12583 v01 S     0:00 -bash
> 26205 pp0 S     0:01 -bash
> 26327 pp0 S     0:03 lynx
> 26380 v01 R     0:00 ps x
>
> I'm ABSOLUTELLY sure the process 26205 started BEFORE process 12583,
> wich is the shell I'm running right now. Again, is this normal?

"ps -u" will tell you when the processes started. One possible
explanation is PID re-use. This seems unlikely, since takes a long
time to get PID re-use on most machines.

Another explanation is that process 12583 is older than the shell it
is running. Since getty uses exec to invoke login, and login uses exec
to invoke your shell, your shell gets the same PID as the original
getty. If that getty has been hanging around for some time, it will
have a low process number. I guess process 26205 was started by
telnetd, or something similar, after you typed telnet (or whatever),
so it will be only slightly older than that shell. This is normal on
all unix systems I know of.

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