[tor-relays] killall -hup command

Hello,

So recently I rebooted my relay using the killall tor -hup command (while I was trying to mae some changes to my torrc file). My relays uptime was not changed at all by this, having a current uptime of about 6 days. However, I noticed today at http://torstatus.blutmagie.de/router_detail.php?FP=db1af6477bb276b6ea5e72132...

My relay lost the stable flag (which it had had for the last about two months). I know not to worry about exactly what flags I have all the time, but it raises the question of what eactly the killall -hup command does?

Thanks.