> i added some welcome message in the /etc/motd file, but everytime when i
> login, i can't see that message.
> which file control this function?

'man login' gives information on this.

  When you login, for Bourne shell and Korn shell logins, the shell executes
/etc/profile and $HOME /.profile, if it exists.

  For C shell logins, the shell executes /etc/.login, $HOME /.cshrc, and
$HOME /.login.

  The default /etc/profile and /etc/.login files check quotas , print
/etc/motd, and check for mail.

None of the messages are printed if the file  $HOME /.hushlogin exists.