TCP Wrappers

using hosts.allow and hosts.deny to control sshd connection in ubuntu

please make sure your hosts.allow works first, or you will lost control after create hosts.deny.

adding your ip range which allow using sshd for example 192.168.0.1/24 :

vi /etc/hosts.allow
sshd: 192.168.0.1/24

deny all other ip using sshd :

vi /etc/hosts.deny
sshd:all

deny all other ip excpet ip range :

vi /etc/hosts.deny
ALL:ALL EXCEPT 192.168.0.1/24

Other useful command :

find program full path by ps -auxwe

ps -auxwe |grep "target pid or port"

find all connection to your machine currently

netstat -tunpla
netstat -tunplac <<< monitoring continuously by adding -c

reference link :