Re: Turn off a PC:Problems on C/S

The recent discussion has gone something like: > cwakins@leia.alloys.rmc.com "Clem Akins" writes: ><snip> >> Buenos dias! >> >> The answer below appeared a while ago, maybe it will help. >> >> _ This problem is caused by not using the SO_KEEPALIVE option on the socket. >> _ If the option is omitted there is no way to tell that the end point >> _ (i.e. PC) is dead. Check out the options for the Q+E driver on how to >> _ set this from the PC side and your problem will disappear. and from sally@excelsis.demon.co.uk: >Can this also apply to any type of networked connection? Can is also >sometimes lead to the 'left-behind' process eventually producing a core >dump & exiting? SO_KEEPALIVE is, as far as I know, a TCP/IP-only option. It is present because on wide area networks it is difficult to tell if the remote site has disappeared or is just taking a while to respond. If SO_KEEPALIVE is enabled at BOTH ends of the connection then what happens is when the server has not heard from the client for a specified period of time if sends a "Are you there?" packet to the client to see if the client is still there. If no reply, it tries again a few times and, presuming no response, closes the processes which were using the socket. On the UNIX systems I have looked at this the server waits for 2 hours before checking on the client. It then sends 5 or 6 "hello" packets spaced at about 5 minute intervals before shutting down the socket. So your "left-behind process" on the server Sally will remain for 2 and a half hours before being closed down (and possibly coredumping - depends on what it was doing when the connection was lost). So, having turned on the option on your Q+E driver (or application on PC) you might also want to tune the KEEPALIVE timeout value on the UNIX server as 2 hours is a bit much if WANs are not involved. I've tuned this parameter down to saying "hello?" after 10 minutes with no noticable affect on network traffic. Hope this helps. E-mail for more info! -- Mark Bradshaw (not) not@hoople.demon.co.uk