[CentOS] I can't connect to /dev/ttyS0

[Keith Roberts]

On Sat, 24 Sep 2011, Michel Donais wrote:

> To: CentOS mailing list <centos at centos.org>
> From: Michel Donais <donais at telupton.com>
> Subject: [CentOS] I can't connect to /dev/ttyS0
> 
> The computer is an HP Proliant DC7600S.
> O/S: Centos 5.7
>
> I try to connect minicom or Hylafax to /dev/ttyS0 and I can't reach the
> modem.
>
> Can somebody had this problem and find a solution?

Hello Michel.

You first need to double-check that /dev/ttyS0 is actually 
the correct serial COM port you have the modem connected to.

I've know the COM port numbers to mysteriously change 
for some reason. My APC UPS was connected and working on 
/dev/ttyS1 and it stopped working recently. The serial COM 
port has changed for some reason to /dev/ttyS0. So I had to 
edit the config file and stop and restart apcupsd, and it's 
working fine again now.

Please look under System->Hardware and then click the 
16550A-compatible COM port in the LH pane.

Then in the RH pane click on 'Advanced', and find the 
serial.device string or linux.device_file.

This will be something like:

linux.device_file  strlist /dev/ttySx where x == 0|1|2|3
serial.device      strlist /dev/ttySx where x == 0|1|2|3

Make sure this is the same as what you are trying to connect to.

Here's a screenshot of Device Manager showing my COM port 
settings:

http://oi56.tinypic.com/2a7h1sp.jpg

If nothing shows under Device Manager settings, please check 
you have your serial COM ports turned on in your BIOS 
settings at reboot time :)

Kind Regards,

Keith Roberts

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