Log files
Useful log files
Main useful one is
/var/log/messages
and contains the majority of the useful information the system produces.
There's some other useful ones depending what you're doing.
Ldap stuff? /var/log/ldap
cron stuff? /var/log/cron
Security/access stuff you'll either want /var/log/secure or maybe stuff in /var/log/sssd/ folder.