On Thursday, 14 March 2019 16:42:53 GMT Patrick Wigmore wrote:
> Could you elaborate on what was involved to 'do things properly'?
Well. In the context of what you're asking, I can't tell you any more than I
have already. although I now realise that I wasn't doing quite what I thought
I was doing.
On the Pi, I opened the Raspberry Pi Configuration tool and enabled the Serial
Port. This enabled the Serial Console. The Pi had previously been configured
to Auto-login to the Pi User's account.
This means that if I attached a normal monitor and keyboard to the Pi, I can
view the boot messages as they come up and then the program that I have set up
to start at boot up ends.
When I view the process using the serial port, exactly the same thing happens,
but the program doesn't start until I've logged in.
> I don't think I understand what enabled you to see the output from
> your program after logging in.
Ah. I'm not sure that I fully understood myself what was going on. See
below.
> I would not expect the output of a running program to appear on a
> terminal without some specific configuration or incantations to tell
> it to do that, especially if you want it to only show up after logging
> in on the terminal. This might be a mistaken assumption on my part.
No. I don't think you are mistaken. Your scepticism made me think about what
I had just done. In fact, what is happening is that I have set the program to
start in .bashrc, so in reality, it is a new instance of the program that
starts when I log in via the serial port; the version started at boot up is
still running and not visible to me. I just modified the program so I could
see that (it was a bit noddy).
> How does getty trigger this program that started on boot to output on
> the terminal after you log in?
See above.
So the news isn't as good as I thought, but restarting the software when I log
in through the serial port isn't going to be a show stopper. I would probably
have to stop the all instances and then restart it to get a true picture of
what is going on. Alternatively I can disable Auto-Login and catch the first
instance. I'll get the information I need, but I will have to work a bit
harder and I won't see the messages that were being written just prior to the
login.
Maybe that miniature HDMI screen isn't such a bad idea ;-)
--
Terry Coles
--
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