Which services will have listening ports on a hardened Linux log server?

RPC exposes unneeded remote procedure call endpoints and SMTP is a mail transfer service, neither of which is required on a dedicated log collection server.

TFTP transmits data in cleartext with no authentication and Telnet provides unencrypted remote shell access, both of which are explicitly prohibited on a hardened system.

SSH provides encrypted, strongly authenticated remote administration and is the accepted secure replacement for plaintext protocols such as Telnet. Syslog (default port UDP/TCP 514) is the core service of a log server, used to receive log messages from network devices and systems across the environment. Together these two services fulfill the operational requirements of a dedicated log server while keeping the attack surface minimal in accordance with server hardening principles.

HTTP transmits data without encryption and is not needed for log collection, while SFTP is a file transfer service that is not a standard component of a syslog server.