I don't know exactly what your problem is, but take into account that bash
only appends its (in-memory) history to .bash_history at exit (so while
the shell is active you won't see any changes)
Actually i never worked on multi user environment. this is the first time that i am dealing with multiple users. i want to monitor what hey are doing. so i thought history is the best option to do.but when i try to scan their history i see nothing. so my Question is why i can not see any thing new in their history file.