hosts.allow和hosts.deny

/etc/hosts.allow : 明確允許
/etc/hosts.deny : 明確拒絕
明確允許優先於明確拒絕

hosts.deny

#
# hosts.deny    This file describes the names of the hosts which are
#       *not* allowed to use the local INET services, as decided
#       by the '/usr/sbin/tcpd' server.
#
sshd : ALL

hosts.allow

#
# hosts.allow   This file describes the names of the hosts which are
#       allowed to use the local INET services, as decided
#       by the '/usr/sbin/tcpd' server.
#
sshd : 127.0.0.1, 127.0.0.2