bro as a daemon.

When i run bro in the background, it seems to die off
without any notice.(There is no log why, in bro.log or /var/log/messages)
i ran as ./bro -i eth1 mt.bro &

Do you know of any reason why ?

This is strange, as we run Bro in the background all the time.

Maybe it would be better to run as a daemon if possible
rather that using the &

No, this is something worth debugging, there's nothing magic about running
as a daemon. The way to go about it is run it in the background, then
attach to it with the debugger, set a breakpoint in "exit", and then see
what's causing it to call exit().