I used boringproxy for years and I recomend you

trough ssh when you connect to your machine run :

lastb -10

This will show you the last 10 login failed attemps you can change to 20 or whatever

you can also run: last -10 to see the last successful logged in

use :

more history

to see all the commands that someone have typed

on the dir /var/logs you have a lot of another logs too

for more paranoid level use

netstat -a

This will show you all incoming and outgoing communications

and like the others said considere using firewall and fail2ban

Note: don’t relly to much on firewalls since they are easy to bypass

keep all softwares updated

read frequently about new vulnerabilities if there is some vulnerability that affects your software until gets patched turn of that service.

you can just use a reverse shell