To check and analyze the rootkit in a computer, there is a lot of tools that perform and one of them are chkrootkit. Normally, its hard to find a single rootkit in the computer because rootkit can hide from been detected by anti-malware tools.
What is Chkrootkit?
As i mentioned above, Chkrootkit is a tools that analyze the computer for rootkit which around 70 types of rootkit will be detected. Chkrootkit can only be used in Linux and Unix Operating System while Windows Operating System will be using other tool to analyze the rootkit in the Operting System
Usage of Chkrootkit
If you need to run the Chkrootkit, you need to type chkrootkit -d . This command will used to debug the system.
Chkrootkit Command

Source: Three tools to scan a Linux server for Malware and Rootkits