新手求救（dovecot configure)

[starxing]

dovecot.conf 如下：
base_dir = /var/run/dovecot/
protocols = imap pop3
log_path = /var/log/dovecot
info_log_path = /var/log/dovecot.info
login_dir = /var/run/dovecot/login
login_chroot = yes
login = imap
login_executable = /usr/lib/dovecot/imap-login
login_user = dovecot
login = pop3
login_executable = /usr/lib/dovecot/pop3-login
valid_chroot_dirs = /var/spool/vmail
default_mail_env = maildir:/home/vmail/%d/%n
#imap_executable = /usr/lib/dovecot/imap
#pop3_executable = /usr/lib/dovecot/pop3
mail_executable = /usr/lib/dovecot/imap
mail_executable = /usr/lib/dovecot/pop3
auth = default
disable_plaintext_auth = no
auth_mechanisms = plain digest-md5
auth_userdb = passwd-file /etc/dovecot/users
auth_passdb = passwd-file /etc/dovecot/passwd
auth_executable = /usr/lib/dovecot/dovecot-auth
auth_user = root
auth_verbose = yes

啟動dovecot: /etc/init.d/dovecot restart

Restarting mail server: dovecotWarning: Ignoring deprecated 'login' section handling. Use protocol imap/pop3 { .. } instead. Some settings may have been read incorrectly.
Warning: Ignoring deprecated 'login' section handling. Use protocol imap/pop3 { .. } instead. Some settings may have been read incorrectly.
Error: Error in configuration file /etc/dovecot/dovecot.conf line 21: Unknown setting: userdb

我查看過dovecot.conf的原文件，但還是不知如何修改該行。
請教這裡該如何修改！

我的系統是：Ubuntu6.10