Re: cannot start detached sessions (with -m -d) back to back

[christos%astron.com@localhost (Christos Zoulas)]

In article <YdDddKJc+XXgwhwu%pony.stderr.spb.ru@localhost>,
Valery Ushakov  <uwe%stderr.spb.ru@localhost> wrote:
>On Sat, Jan 01, 2022 at 21:49:00 +0000, RVP wrote:
>
>> OK, but, I think we can do better than rudely sending processes a SIGHUP.
>> Using the BSD-native /dev/ptm device (via openpty(3) & friends) instead of
>> /dev/ptmx seems to do the right thing: EOF when the PTY master is closed.
>> 
>> File a PR (Category: pkg)
>
>Why pkg?  This is a kernel bug.  POSIX doesn't seem to say anything
>about this, but Christos pointed out e.g. 
>
>  https://docstore.mik.ua/manuals/hp-ux/en/B2355-60130/pty.7.html
>
>that says
>
>  A read() request made on the slave side of a pty after the master
>  side is closed returns 0 bytes. Closing the master side of a pty
>  sends a SIGHUP hangup signal to the tty process group number of the
>  corresponding slave side and flushes pending input and output.
>
>Solaris docs for (STREAMS-based) ptys say:
>
>  When the master device is closed, an M_HANGUP message is sent to the
>  slave device to render the device unusable. The process on the slave
>  side gets the errno ENXIO when attempting to write on that stream,
>  but it will be able to read any data remaining on the stream head
>  read queue. When all the data has been read, read(2) returns 0,
>  indicating that the stream can no longer be used.

Yes, in the end screen was at fault for setting CLOCAL in the pty which
prevented from SIGHUP from being sent. I fixed it.

christos