HUP doesn't send to processes when logout

[平天韩]

hi,

It seems that when I logout from the console, the background process
doesn't get HUP signal:
{ trap "echo Ignore HUP >>/tmp/trap.out" 1; while sleep 3;do echo
hello >>/tmp/hello.txt;done; }&
And it seems it will become a daemon and run forever until rebooting.
Is this correct? Why it didn't get HUP signal?

Thanks!