Ubuntu 18.04.6 LTS (Bionic Beaver) / Ubuntu 20.04.3 LTS (Focal Fossa) - Common Commands

Ubuntu 18.04.6 LTS (Bionic Beaver) / Ubuntu 20.04.3 LTS (Focal Fossa) - Common Commands & Frequent Tasks

Allowing Incoming Traffic on Specific Ports

sudo iptables -A INPUT -p tcp --dport ssh -j ACCEPT

or

sudo iptables -I INPUT 6 -m state --state NEW -p tcp --dport 80 -j ACCEPT
sudo netfilter-persistent save

List Iptable rules

sudo iptables -L

Save iptables rules

sudo sh -c "iptables-save > /etc/iptables.rules"

Apply rules

sudo iptables-apply /etc/iptables.rules

Disabling the firewall - iptables

If you need to disable the firewall temporarily, you can flush all the rules using

sudo iptables -P INPUT ACCEPT
sudo iptables -P OUTPUT ACCEPT
sudo iptables -P FORWARD ACCEPT
sudo iptables -F

Delete Iptables rule by line number

sudo iptables -L --line-numbers

sudo iptables -D INPUT 3

Disabling the firewall - UFW

systemctl stop ufw
systemctl disable ufw

iptables-persistent

sudo apt-get install iptables-persistent
sudo netfilter-persistent save

Disable swap

sudo swapoff -a

SSH

ssh-keygen -t rsa

nano ~/.ssh/authorized_keys
nano /etc/ssh/sshd_config
systemctl restart sshd