Chk-rootkit is a simple program that checks your server for known rootkits, helping detect sniffers, trojans, worms, and other back-door programs.
Start by making sure we are up to date.
$ sudo apt-get update && sudo apt-get upgrade -y
New we will install chkrootkit:
$ sudo apt install chkrootkit -y
$ sudo nano /etc/chkrootkit.conf
You will see the following:
RUN_DAILY="false"
RUN_DAILY_OPTS="-q"
DIFF_MODE="false"
Change it to:
RUN_DAILY="true"
RUN_DAILY_OPTS="-q"
DIFF_MODE="false"
Now save the file by hitting [CTRL-X] then Y, then [ENTER]