Problem statement
What should I change first when SSH login on CentOS 7 takes too long before the password prompt appears?
Start by disabling UseDNS and GSSAPIAuthentication in sshd_config, because those are the two most common sources of login delay on older CentOS 7 hosts. If the host also has broken or slow IPv6 reachability, pinning AddressFamily inet can remove another common wait state.
Treat this as a safe first-pass optimization before looking at PAM, fail2ban, auth logs, or network path issues. The goal is to eliminate the common daemon-side stalls first.
What to check
- Turn off reverse DNS lookup with UseDNS no.
- Disable unused Kerberos/GSSAPI auth with GSSAPIAuthentication no.
- Use AddressFamily inet when IPv6 fallback is hurting login latency.
Parent topic
Keep legacy CentOS 7 hosts installable and maintainable when yum repositories fail, mirrors expire, or Docker data needs to be moved off a crowded disk.