Re: failure to login on serial console

[Chet Ramey]

On 2/3/21 9:04 AM, Alain D D Williams wrote:
> The problem that I have seems much the same as from Feb 2019:
>
> https://www.mail-archive.com/bug-bash@gnu.org/msg22665.html

Yes, it's the same.

> Try to login on a serial console, see the message:
>
> bash: initialize_job_control: no job control in background: Bad file descriptor

This means that the bash process is not in the same process group as the
terminal, and nothing changes the situation after it's gotten SIGTTIN 16
times. Bash-4.4 ignored the situation, and just waited until it resolved
itself (which might never happen); bash-5.0 tries to avoid hangs and warns
you about what it's doing.

So your shell is not running in the same process group as the terminal,
and has no access to read from its controlling terminal.

> When I press any key I get logged out. This is what happens when I press the
> key:
>
> # strace -p 19149
> strace: Process 19149 attached
> pselect6(1, [0], NULL, NULL, NULL, {[], 8}) = 1 (in [0])
> read(0, 0x7ffc8237730f, 1)              = -1 EIO (Input/output error)

And this is what happens. When you try to read from a background process,
the read returns -1/EIO since bash is ignoring SIGTTIN by this point.

--
``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU    chet@case.edu    http://tiswww.cwru.edu/~chet/