[Debconf-devel] Bug#1061480: debconf should automatically be noninteractive if input is /dev/null

[Josh Triplett]

Colin Watson wrote:
> Sorry for my long delay in replying to this.

No problem; thank you for the response!

> On Mon, Sep 30, 2024 at 02:47:53PM -0700, Josh Triplett wrote:
>> I've written a draft patch for this, at
>> https://salsa.debian.org/pkg-debconf/debconf/-/merge_requests/18 . I've
>> also attached it here.
>> 
>> I'm happy to try other approaches for this, as well; this was the
>> simplest.
>
> I'm trying to understand what's going on with the original setup before
> going ahead with this.  Your original report shows that the Readline
> frontend (based on Teletype) is being used, but
> Debconf::FrontEnd::Readline already has a `-t STDIN` check.  So your
> commit message comments about not having a TTY don't seem quite
> accurate: it looks as though the situation is that you _do_ have a TTY
> (at least enough for `-t STDIN` to succeed) but that it's broken and
> reads from it always return EOF.  Does this sound right?  (It sounds
> quite weird to me, and might point to a bug in your setup.)

No, my setup has stdin as /dev/null, and stdout/stderr as UNIX sockets, and no controlling TTY. (And, as you guessed, TERM unset.)

Note in particular that it's necessary to have no controlling TTY and have /dev/tty not exist, to avoid debconf's fallbacks that try to find a terminal to use.

Apologies for posting a transcript that didn't match the description of the bug I was reporting. The actual issue I was observing was with the teletype frontend, not the readline frontend.

(The transcript is from a different, related issue. I expect that 723843 might fix that one.)

> It would be helpful for me to have a reproducer for this.  If I just try
> `env -u TERM apt install tzdata </dev/null`, I get behaviour that, while
> somewhat buggy, is not the same as what you reported and doesn't result
> in a hang:

I'll follow up with the right transcript.

>   Setting up tzdata (2024b-4) ...
>   debconf: unable to initialize frontend: Dialog
>   debconf: (TERM is not set, so the dialog frontend is not usable.)
>   debconf: falling back to frontend: Readline
>   debconf: unable to initialize frontend: Readline
>   debconf: (This frontend requires a controlling tty.)
>   debconf: falling back to frontend: Teletype
>   Configuring tzdata
>   ------------------
>  
>   Please select the geographic area in which you live. Subsequent configuration
>   questions will narrow this down by presenting a list of cities, representing
>   the time zones in which they are located.
>  
>     1. Africa   3. Antarctica  5. Asia      7. Australia  9. Indian    
> 11. Etc
>     2. America  4. Arctic      6. Atlantic  8. Europe     10. Pacific
>   Geographic area:
>   Use of uninitialized value $_[1] in join or string at 
> /usr/share/perl5/Debconf/DbDriver/Stack.pm line 112.
>  
>   Current default time zone: '/UTC'
>   Local time is now:      Sun Dec 29 14:35:42 UTC 2024.
>   Universal Time is now:  Sun Dec 29 14:35:42 UTC 2024.
>   Run 'dpkg-reconfigure tzdata' if you wish to change it.
>  
>   Use of uninitialized value $val in substitution (s///) at 
> /usr/share/perl5/Debconf/Format/822.pm line 84, <GEN6> line 4.
>   Use of uninitialized value $val in concatenation (.) or string at 
> /usr/share/perl5/Debconf/Format/822.pm line 85, <GEN6> line 4.
>
> #723843 is also somewhat related here, although without a reproducer I'm
> not quite sure whether it would fix your problem.
>
> Thanks,
>
> -- 
> Colin Watson (he/him)                              [cjwatson at debian.org]