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

[Michael Biebl]

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


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