Serial port numbers changing at each boot

Frans Ketelaars ketelaars at
Sat Jul 10 21:26:15 UTC 2010

On Thu, 08 Jul 2010 19:46:20 +0300, Dotan Cohen wrote:

> A machine with a Gigabyte g33 motherboard and two serial expansion cards
> has an interesting situation in which on each boot the serial ports get
> different tty numbers. Why should they change on each boot, and how can
> I prevent that?
> The machine is currently running Ubuntu 10.04. I had run various Ubuntus
> and Debians without issue in the past. Thanks. says :

"This does not set the I/O address and IRQ in the hardware itself (which 
is set by jumpers or by plug-and-play software). Thus which physical port 
corresponds to say ttyS1 depends both on what the serial driver thinks 
(per setserial) and what is set in the hardware."

Maybe the Ubuntu 10.04 plug-and-play software doesn't consistently 
determine which should be considered the 'first' card ?

Good luck!


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