When `serialhdl` opens a terminal device it must prevent the device from
becoming the controlling terminal of `klippy`, as such a terminal will
send additional messages to the session leader, e.g. a SIGHUP, which
would kill `klippy`. See e.g. #3981.
pySerial already does this, but for e.g. `klipper_mcu` we were not doing
this ourselves.
On Linux a process must set `O_NOCTTY` when opening any file that could
potentially be a terminal device, to avoid this.
Earlier process daemonization tools prevent this from being an issue by
double forking, but under `systemd` a process must take steps to avoid
opening a controlling terminal.
Signed-off-by: Lasse Dalegaard <dalegaard@gmail.com>
Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
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