rkhunter (Rootkit Hunter) is a Unix-based tool that scans for rootkits, backdoors and possible local exploits. It does this by comparing SHA-1 hashes of important files with known good ones in online database, searching for default directories (of rootkits), wrong permissions, hidden files, suspicious strings in kernel modules, and special tests for Linux and FreeBSD.
Step 1. Installation
apt-get install rkhunter
Step 2. How to use rkhunter
After install you can use rkhunter to scan your linux for rootkits with command: