Two instances of PiDP-11 running ?

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Paulo Rebordão

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Apr 2, 2026, 6:09:54 PM (yesterday) Apr 2
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I seem to have 2 instances of PiDP-11 running at the same time.

Captura de ecrã 2026-04-02 230824.png
Or is it normal ?
I have a line "pdp11control start" in /etc/rc.local
and nothing regarding pidp11 on my .profile


Johnny Billquist

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Apr 2, 2026, 6:19:02 PM (yesterday) Apr 2
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I only see one server11 and one client11.

  Johnny

Paulo Rebordão

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Apr 2, 2026, 6:34:09 PM (yesterday) Apr 2
to Johnny Billquist, [PiDP-11]
But there are 2 pids for each? 


Paulo Rebordão


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Bert Driehuis

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Apr 2, 2026, 7:09:07 PM (yesterday) Apr 2
to Paulo Rebordão, Johnny Billquist, [PiDP-11]
Johnny probably meant that on his machine, he only ever saw one at a time.

You have two sessions, one on pts/1 and the other on pts/2. Not sure how you logged on to the device (SSH maybe?), but you appear to have started the emulator on two separate sessions.

This can't possibly do what you want to do, so either logging out or killing one of the sessions or rebooting look like good options at this stage.

-- Bert

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Paulo Rebordão

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Apr 2, 2026, 7:44:40 PM (yesterday) Apr 2
to [PiDP-11]
I can't understand what's going on...
Starting from cold when I first log with user pi, the 2 instances are already running

Bert Driehuis

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Apr 2, 2026, 7:56:38 PM (yesterday) Apr 2
to Paulo Rebordão, [PiDP-11]
Ah, I see... Still. You're somehow trying to start two sessions on those two pseudo terminals. If they're screen based, see if you have two startup scripts each trying to fire up pidp11.

-- Bert

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Johnny Billquist

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4:01 AM (18 hours ago) 4:01 AM
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Seems I failed to reply to the list...

There is only one client11 and one server11 that I can see. The lines
starting with sudo are actually running sudo, not anything directly a
part of the PiDP-11.

Why there are two each of those is another question, but that's sortof
secondary anyway.

Johnny
> Captura de ecrã 2026-04-02 230824.png
> Or is it normal ?
> I have a line "pdp11control start" in /etc/rc.local
> and nothing regarding pidp11 on my .profile
>
>
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|| on a psychedelic trip
email: b...@softjar.se || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol

Paulo Rebordão

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6:12 AM (16 hours ago) 6:12 AM
to Johnny Billquist, [PiDP-11]
Also failed to reply to the list... 

That's weird. 
If you look at the ppid's you'll see that each sudo - client and server - apparently spawn the second ones. 
What could cause that 


Paulo Rebordão


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Bert Driehuis

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6:50 AM (15 hours ago) 6:50 AM
to Paulo Rebordão, Johnny Billquist, [PiDP-11]
You do not give enough information to know what is attached to the other end of pts/1 and pts/2. The scripts many people use start the simulator in a screen(1) session, but there are a number of other ways you can wind up with such pseudoterminals (I have seen people using passwordless SSH to fire up stuff, for example). One possible explanation is that you have a startup script (in /etc/init.d, /etc/rc.local or via systemd), and a functionally identical script that's being called from a .profile or a .bashrc. Or maybe even two startup scripts, or one startup via screen and another via SSH.

It's hard to diagnose from a distance, but you'll have to hunt for duplicate invocations of the emulator, using scripts like rc.pidp11 or pdp11control.sh.

Two commands that may give you a head start:
  sudo find /etc /home/*/.??* -type f -exec grep -E 'pidp11.sh|pdp11control.sh' {} +
  systemctl list-units | grep dp11
... but, what with all the different sites recommending different ways of setting things up, all bets are off!

With kind regards,

-- Bert



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Johnny Billquist

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10:19 AM (12 hours ago) 10:19 AM
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I don't know why the first sudo went into the second sudo. There could
be a number of reasons.

If I were you, I'd start by looking at pidp11.sh and understand what it
is doing, and how it can do what it does. I don't have whatever version
of pidp-11 that you are running, so I can't really comment on this.

But in the end, there is only one client11 and one server11, so no -
there are not two instances of PiDP-11 running.

Johnny

On 2026-04-03 12:11, Paulo Rebordão wrote:
> Also failed to reply to the list...
>
> That's weird.
> If you look at the ppid's you'll see that each sudo - client and server
> - apparently spawn the second ones.
> What could cause that
>
>
> Paulo Rebordão
>
>
> A sexta, 3/04/2026, 09:01, Johnny Billquist <b...@softjar.se
> <mailto:b...@softjar.se>> escreveu:
>
> Seems I failed to reply to the list...
>
> There is only one client11 and one server11 that I can see. The lines
> starting with sudo are actually running sudo, not anything directlya
> part of the PiDP-11.
>
> Why there are two each of those is another question, but that's sortof
> secondary anyway.
>
>    Johnny
>
> On 2026-04-03 01:56, Bert Driehuis wrote:
> > Ah, I see... Still. You're somehow trying to start two sessions
> on those
> > two pseudo terminals. If they're screen based, see if you have two
> > startup scripts each trying to fire up pidp11.
> >
> > -- Bert
> >
> > On Fri, Apr 3, 2026, 01:46 Paulo Rebordão <pjreb...@gmail.com
> <mailto:pjreb...@gmail.com>
> > <mailto:pjreb...@gmail.com <mailto:pjreb...@gmail.com>>> wrote:
> >
> >     I can't understand what's going on...
> >     Starting from cold when I first log with userpi, the 2 instances
> >     are already running
> >
> >     A sexta-feira, 3 de abril de 2026 à(s) 00:09:07 UTC+1, Bert
> Driehuis
> >     escreveu:
> >
> >         Johnny probably meant that on his machine, he only ever
> saw one
> >         at a time.
> >
> >         You have two sessions, oneon pts/1 and the other on
> pts/2. Not
> >         sure how you logged on to the device (SSH maybe?), but you
> >         appear to have started the emulator on two separate sessions.
> >
> >         This can't possibly do what youwant to do, so either
> >         logging out or killing oneof the sessions or rebooting look
> >         like good options at this stage.
> >
> >         -- Bert
> >
> >         On Fri, 3 Apr 2026 at 00:46, Paulo Rebordão
> <pjreb...@gmail.com <mailto:pjreb...@gmail.com>>
> >         wrote:
> >
> >             But there are 2 pids for each?
> >
> >
> >             Paulo Rebordão
> >
> >
> >             A quinta, 2/04/2026, 23:19, Johnny Billquist
> >             <b...@softjar.se <mailto:b...@softjar.se>> escreveu:
> >
> >                 I only see one server11 and one client11.
> >
> >                    Johnny
> >
> >
> >                 Den3 april 2026 00:09:54 CEST, "Paulo Rebordão"
> >                 <pjreb...@gmail.com <mailto:pjreb...@gmail.com>>
> skrev:
> >
> >                     I seem to have 2 instances of PiDP-11 running
> at the
> >                     same time.
> >
> >                     Captura de ecrã 2026-04-02 230824.png
> >                     Or is it normal ?
> >                     I have a line "pdp11control start" in /etc/
> rc.local
> >                     and nothing regarding pidp11 on my .profile
> >
> >
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> email: b...@softjar.se <mailto:b...@softjar.se>             ||
> Reading murder books
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>
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Paulo Rebordão

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1:04 PM (9 hours ago) 1:04 PM
to [PiDP-11]
I attach my pidp11.sh below. There's a loop inside where the client and server are invoked.
Could it be that it's running twice ?

pidp11.sh

John D. Bruner

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1:38 PM (8 hours ago) 1:38 PM
to Paulo Rebordão, [PiDP-11]
As Johnny said, there is only one instance of ./server11 (and of ./client11).

The use of two sudo processes with different ptys, one of which is the parent of the other, is by design. Here's the relevant excerpt from the sudo(8) manpage:

 Process model
       There are two distinct ways sudo can run a command.

       If  an I/O logging plugin is configured to log terminal I/O, or if the security policy explicitly requests it,
       a new pseudo-terminal (“pty”) is allocated and fork(2) is used to create a second sudo process, referred to as
       the monitor.  The monitor creates a new terminal session with itself as the leader and the pty as its control‐
       ling terminal, calls fork(2) again, sets up the execution environment as described above, and  then  uses  the
       execve(2)  system  call to run the command in the child process.  The monitor exists to relay job control sig‐
       nals between the user's terminal and the pty the command is being run in.  This makes it possible  to  suspend
       and  resume  the command normally.  Without the monitor, the command would be in what POSIX terms an “orphaned
       process group” and it would not receive any job control signals from the kernel.  When the command exits or is
       terminated by a signal, the monitor passes the command's exit status to the main sudo process and exits.   Af‐
       ter  receiving  the command's exit status, the main sudo process passes the command's exit status to the secu‐
       rity policy's close function, as well as the close function of any configured audit plugin, and  exits.   This
       mode is the default for sudo versions 1.9.14 and above when using the sudoers policy.


...

Try running "sudo sleep 1000" and you'll see two sudo processes and one sleep.

--John
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Paulo Rebordão

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2:04 PM (8 hours ago) 2:04 PM
to [PiDP-11]
Understood finally. I didn't know of that possible behavior.
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