If not, go to Terminal (Ctrl-Alt-t) and type in the following and press Enter
Code:
sudo ufw enable
You will be prompted for your password, when you type it in there will be no movement (security), but when entered, you will be rewarded with a message that your firewall has been enabled, and that a small script has been generated which will run every time you start the computer.
Between this safeguard, and having a firewall on your (modem-)router, many Linux users do not feel a need to install AV software, myself included.
I run Linux Mint 18.3.....which is a derivative of Ubuntu
In the time I have run Linux, I have never encountered any malware/behaviour etc etc that has made me wish I had an AV installed
At one time, I did install clamav , and instantly regretted it. Poor performance, unstable/weird behaviour......I uninstalled Linux mint and started afresh with a clean install.....and have never regretted that decision.
I do realise that the first thing a windows user will look for is some form of protection....av etc etc
1. enable firewall
2. Make your browser safe (malwearebytes have an addon which will protect you from adds/clickbait/malware/scams.......HERE )
3. Practice safe browsing.
Enjoy your Linux/Ubuntu/whichever distro you happen to have......without the 'drag' of an av.
I cannot give an opinion about apparmour. Others may help here re its effectiveness/effect on system etc etc
@arabmoni, your question is not related to the topic of this thread. Please open a new thread to ask your questions, and we will try to answer you there. The "General Linux" forum or the "Getting Started" forum would both be a good place for you to begin. Thanks!