about history
 

if I up two bash at the same time,
only one of the command history will be recorded
(actually ,I think it's the last-closed one)
how could I remain all the bash's history?

By re-writing bash to save the history after each command
and appending it, rather than reading the lot and writing it
on exit/logout.

You could have a play with the histappend shopt, I've
never used it myself, and I'm not sure what it does :)


Cheers,
Tink