A guide by Unixcop explains how to install Chkrootkit on Ubuntu 20.04 or 22.04 LTS.

How To Install Chkrootkit on Ubuntu 20.04 | 22.04 LTS

In this guide, we will show you how to install Chkrootkit in Ubuntu systems. chkrootkit (Check Rootkit) is a common Unix-based program intended to help system administrators check their system for known rootkits. It is a shell script using common UNIX/Linux tools like the strings and grep commands to search core system programs for signatures and for comparing a traversal of the /proc filesystem with the output of the ps (process status) 

How To Install Chkrootkit on Ubuntu 20.04 | 22.04 LTS - Unix / Linux the admins Tutorials