Guide: https://netwayfind.github.io/cp-lockdown/

Checklist: Linux
__:___ read readme/instructions
Users and Groups
__:___ verify local user accounts
__:___ verify local user groups
__:___ disable guest access
__:___ review sudo permissions
Network resources
__:___ firewall (iptables)
__:___ monitor network connections (netstat)
Installation cleanup
__:___ check Applications
__:___ check Services
__:___ retrieve and install latest updates (apt-get)
Scans
__:___ chkrootkit
__:___ rkhunter
Filesystem
__:___ find and remove unauthorized files (e.g. pictures, music, programs)
__:___ check /etc/hosts file
__:___ check filesystem permissions
Configuration
__:___ install auditd
__:___ install boot-up manager
__:___ review cron jobs
__:___ install libpam-cracklib
__:___ password policy
__:___ account lockout policy
__:___ configure required services and programs
Logs
__:___ System logs