How to secure your Linux ?

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There are four common and useful methods for you to secure and check your Linux.

• Port Scan
• Firewall
• Update Security package
• Antivirus

Port Scan

You can check your system by scanning your port number. Once you find out some ports that are open and not used, remember to close them and stop their related services accordingly.

• Install port scan tool
  sudo install nmap
  
• Execute Port Scan command to scan Port from 1 to 65535
  nmap -p 1-65535 -T4 -A -v [Target IP]
  

Firewall

The fundamental rule to improve the security of your Linux is your system merely opens necessary and required ports for your services. I strongly recommend you to set up restrictions on port 22 to avoid being attacked by SSH Brute Force. Hopefully, DenyHost is a smart firewall that can automatically parse SSH Log and detect malicious IPs to setup block rules for you. 

• Install DenyHost

Update Security package

Update your system with latest security packages automatically.

Install this package if it isn't already installed using
sudo apt-get install unattended-upgrades

To enable it type
sudo dpkg-reconfigure unattended-upgrades

and select "yes".

AntiVirus

Scan and check your system regularly with the following antivirus software.

• Install Virus
  sudo apt-get install clamav
  
• Update Virus code
  sudo freshclam
  
• Scan system
  sudo clamscan --remove=yes -i -r ./