Bug#977562: systemd: Incorrect order of agetty arguments in serial-getty at ttyS0.service definition file

[Marcin Krol]

Well, I hoped that you'd simply change that order in the service file 
(I'm new to this, do you expect me to produce patch or something like 
that?). Otherwise serial comm doesn't work, at least for me.




On 1/14/21 3:06 PM, Michael Biebl wrote:
> Am 19.12.20 um 16:47 schrieb Andreas Henriksson:
>> Control: tags -1 + moreinfo
>>
>> On Wed, Dec 16, 2020 at 11:39:06PM +0100, Michael Biebl wrote:
>>> Am 16.12.20 um 20:49 schrieb MK:
>>>> Package: systemd
>>>> Version: 241-7~deb10u5
>>>> Severity: normal
>> [...]
>>>> Incorrect order of arguments to agetty in the 
>>>> serial-getty at ttyS0.service
>>>> unit file.
>>>>
>>>> It is:
>>>>
>>>> ExecStart=/sbin/agetty --autologin root -8 --keep-baud 
>>>> 115200,38400,9600 ttyS0 xterm-256color
>>>>
>>>>
>>>> While it should be like:
>>>>
>>>> ExecStart=/sbin/agetty --autologin root -8 --keep-baud ttyS0 115200 
>>>> xterm-256color
>> [...]
>>> According to the examples in man agetty, both should work.
>>>
>>> Andreas, can you comment here?
>>> If what MK is saying, should the "EXAMPLE" section in man agetty be 
>>> updated?
>>>
>>
>> I don't really have much prior knowledge about *getty, but in my past
>> experience with other util-linux tools it is often the case that
>> (likely for historical reasons/compatibility) the arguments that
>> doesn't come in a dash-form is attempted to be accepted in either
>> order based on guessing which one was specified. In my past experience
>> something that was guessable in the past might in later years become
>> sometimes impossible to correctly guess right, so sticking with
>> what synopsis describes is usually the safest as far as I'm concerned.
>>
>> In the agetty case, the guessing is done here:
>> https://sources.debian.org/src/util-linux/2.36.1-2/term-utils/agetty.c/#L897 
>>
>>
>> is_speed basically checks if the current argument only consists of
>> either 0-9 or ','.
>>
>> It is not obvious to me how it could go wrong in the example originally
>> described in this bug report.
>>
>> Please also note that for example sysvinit's inittab also uses getty
>> with arguments in both orders.
>>
>> Simply it should work either way.
>>
>> Please also note that the argument order is not the only thing changed.
>> It was also changed from specifying 3 speeds to only 1.
>>
>> Maybe the real issue here is that line speed detection isn't working?
>> I'd appreciate if the bug reporter could dive a bit deeper into the
>> problem.
> 
> 
> @MK any further feedback? Otherwise I would close this bug report.
> 
> Regards,
> Michael
> 
>