Chkrootkit is a popular security scanner that helps administrators look for signs when a system is infected with rootkits. You can use chkrootkit to find files and rules associated with rootkits, but you cannot be 100% sure that all rootkits will be found
Rootkits are malicious tools attackers install to keep persistent, stealthy access to a compromised system. Regular rootkit scanning is an essential part of server security hygiene — especially for cloud servers that run public services.
Lynisis a free, open-source, powerful, and popular security auditing and scanning tool for Unix/Linux-like operating systems. It is a malware scanning and vulnerability detecting tool that scans systems for security information and issues, file integrity,
Rootkit Hunter (rkhunter) is a Unix-based tool that scans for rootkits, backdoors and possible local exploits. Rootkits are self-hiding toolkits secretly installed by a malicious intruder to allow that user to gain access to the server.