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Avoid rebooting server to gain back RS232 connection

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  Avoid rebooting server to gain back RS232 connection john doe <johndoe65534@mail.com> - 2021-12-01 09:20 +0100
    Re: Avoid rebooting server to gain back RS232 connection deloptes <emanoil.kotsev@deloptes.org> - 2021-12-01 10:30 +0100
    Re: Avoid rebooting server to gain back RS232 connection Charles Curley <charlescurley@charlescurley.com> - 2021-12-01 15:40 +0100
      Re: Avoid rebooting server to gain back RS232 connection Joe <joe@jretrading.com> - 2021-12-01 17:10 +0100
        Re: Avoid rebooting server to gain back RS232 connection john doe <johndoe65534@mail.com> - 2021-12-03 08:10 +0100

#242562 — Avoid rebooting server to gain back RS232 connection

Debians,

I'm using a RS232 cable to connect to a server everything is properly
set up and works fine.
For some reasons I lost the connection to my server that is I can not
control the server using serial console.
If I reboot that server I can once again manage that server using serial
console.

Is there a way to get back the connection without having to reboot the
server?

In other words, how can I reconnect when the cable has been disconnected

Any feedback is welcome..

--
John Doe

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#242569

john doe wrote:

> I'm using a RS232 cable to connect to a server everything is properly
> set up and works fine.
> For some reasons I lost the connection to my server that is I can not
> control the server using serial console.
> If I reboot that server I can once again manage that server using serial
> console.
> 
> Is there a way to get back the connection without having to reboot the
> server?
> 
> In other words, how can I reconnect when the cable has been disconnected

Above you say for some reason and now you say cable was disconnected.
If it is a straight forward RS232 on the mainboard of the server and you are
using something like minicom, you just need to reconnect to the device
(after attaching the cable).
If you have an issue with that, you need to debug what is going on.
IF you have the rs232 serial as module, you can try SSH to the server and
rmmod/insmod or modprobe ... but if you could SSH why would you RS232 to
the server?
Anyway ... based on the scare information, this is the only thing that came
into my mind.

BR

-- 
FCD6 3719 0FFB F1BF 38EA 4727 5348 5F1F DCFE BCB0

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#242571

On Wed, 1 Dec 2021 09:14:11 +0100
john doe <johndoe65534@mail.com> wrote:

> I'm using a RS232 cable to connect to a server everything is properly
> set up and works fine.
> For some reasons I lost the connection to my server that is I can not
> control the server using serial console.

...

> 
> In other words, how can I reconnect when the cable has been
> disconnected

The first thing I would do is find out why your cable is being
disconnected, and see to it that it does not happen again.

But why RS-232? Why not SSH over Internet Protocol (IP)? If it's a
server, it should have some sort of networking.


-- 
Does anybody read signatures any more?

https://charlescurley.com
https://charlescurley.com/blog/

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#242572

On Wed, 1 Dec 2021 07:10:49 -0700
Charles Curley <charlescurley@charlescurley.com> wrote:

> On Wed, 1 Dec 2021 09:14:11 +0100
> john doe <johndoe65534@mail.com> wrote:
> 
> > I'm using a RS232 cable to connect to a server everything is
> > properly set up and works fine.
> > For some reasons I lost the connection to my server that is I can
> > not control the server using serial console.  
> 
> ...
> 
> > 
> > In other words, how can I reconnect when the cable has been
> > disconnected  
> 
> The first thing I would do is find out why your cable is being
> disconnected, and see to it that it does not happen again.
> 
> But why RS-232? Why not SSH over Internet Protocol (IP)? If it's a
> server, it should have some sort of networking.
> 
> 

Original information is indeed scarce. The OP mentions using a serial
console, but that may have been for troubleshooting, and we do not know
if the console is the usual client.

Many proper servers have at least an option of an RS-232 connection
into the BIOS or equivalent, allowing remote control of BIOS parameters
and rebooting when necessary. It's an unfitted option on my HP
microserver. Many UPS devices have an RS-232 connection to a server to
notify of loss of mains, low battery etc. SSH would not normally be an
alternative for these functions.

Serial may be ancient, but it still has its uses, particularly with
PIC/Arduino-level home-made peripherals. Not every job requires a
Raspberry Pi. As it happens, one of the functions of my home server is
to record outside temperatures from a radio link. That's done with
RS-232 (more accurately, RS-485 simplex, there is little genuine 25-pin
RS-232/V24 hardware around now) because that's what the radio module
provides, and indeed, what the original temperature sensor produces.

I'd agree, the ideal solution would be to fix the disconnections, but
troubleshooting the occasional drop of a serial link is not a trivial
matter. One assumes the receiver is resetting for some reason, as
asynchronous serial ('RS-232') doesn't actually have the concept of
'connection', and if the signal is lost or temporarily corrupted, will
just pick up again when valid signals resume and the receiver can
re-sync. It should be possible to literally pull the plug out of an
async serial stream, replug it and have the stream recover after a
couple of failed re-syncs. This is clearly not happening here.

-- 
Joe

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#242644

On 12/1/2021 5:00 PM, Joe wrote:
> On Wed, 1 Dec 2021 07:10:49 -0700
> Charles Curley <charlescurley@charlescurley.com> wrote:
>
>> On Wed, 1 Dec 2021 09:14:11 +0100
>> john doe <johndoe65534@mail.com> wrote:
>>
>>> I'm using a RS232 cable to connect to a server everything is
>>> properly set up and works fine.
>>> For some reasons I lost the connection to my server that is I can
>>> not control the server using serial console.
>>
>> ...
>>
>>>
>>> In other words, how can I reconnect when the cable has been
>>> disconnected
>>
>> The first thing I would do is find out why your cable is being
>> disconnected, and see to it that it does not happen again.
>>
>> But why RS-232? Why not SSH over Internet Protocol (IP)? If it's a
>> server, it should have some sort of networking.
>>
>>
>
> Original information is indeed scarce. The OP mentions using a serial
> console, but that may have been for troubleshooting, and we do not know
> if the console is the usual client.
>
> Many proper servers have at least an option of an RS-232 connection
> into the BIOS or equivalent, allowing remote control of BIOS parameters
> and rebooting when necessary. It's an unfitted option on my HP
> microserver. Many UPS devices have an RS-232 connection to a server to
> notify of loss of mains, low battery etc. SSH would not normally be an
> alternative for these functions.
>

As Joe has hinted out, I use RS232 for debugging when I screw up my
network!!! :)

After having rebooting the server, I can confirm that plugging and
unplugging the cable works.
I'm not sure what was mest up there but all is well now!

Regarding the involuntary disconnection,, the cable was not properly
inplace which is now the case.

Thanks all for the help.

--
John Doe

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