Small settings that cause confusion when wrong.
HOSTNAME
Set a fully qualified hostname, such as server1.yourdomain.com, and ensure it resolves in DNS.
Mail servers in particular check this. A server announcing itself with an unresolvable hostname has mail rejected.
Set it in the system configuration and in the hosts file.
REVERSE DNS
The address should resolve back to the hostname. This is set by whoever controls the IP address block, so open a ticket with the hostname you want.
Mismatched forward and reverse DNS is a common cause of mail deliverability problems.
TIMEZONE
Set it to your local timezone, or to UTC if you operate across regions and prefer consistent logs.
Whichever you choose, know which it is. Reading logs while assuming the wrong timezone wastes considerable time during an incident.
LOCALE
Affects character encoding and date formats. Set it appropriately, particularly if your applications handle non-ASCII text.
WHY THESE MATTER
Wrong timezone makes log correlation impossible. Wrong hostname breaks mail. Both are two-minute fixes that cause hours of confusion later.
