system password's file

[iwan at staff.usd.ac.id]

Hi all,
I want to migrate from linux to freebsd. My linux box
(mail server) have alot of user (hundreds) --this is the
problem. I dont know which file which the password's file.
I dont want typing user name and its password one by one.
Beside of that, thereis possibly my users change  their
passwords.
How can I do this migrating ? (save)
I'm sorry my English is not good.

Thanks before.
regrds.