The server rejected an unsupported or misspelled protocol option during the connection handshake, producing error 63 (EE_UNKNOWN_PROTOCOL_OPTION).
MySQL Error 63: EE_UNKNOWN_PROTOCOL_OPTION appears when the client or server sends an option the MySQL protocol does not recognize. Confirm option spelling, upgrade outdated clients, and remove unsupported variables to resolve the issue.
Unknown option to protocol: %s. EE_UNKNOWN_PROTOCOL_OPTION was added in 8.0.13.
Error 63 (EE_UNKNOWN_PROTOCOL_OPTION) is raised by the MySQL server when it encounters an unrecognized capability or system variable during the connection handshake. MySQL 8.0.13 introduced this check to guard against malformed or outdated client requests.
The server closes the connection immediately, so applications see a generic connection failure. Understanding which option triggered the fault is essential for a permanent fix.
The error surfaces during the initial handshake - before authentication finishes.
It typically follows a recent server upgrade, client downgrade, or manual change to connection flags such as compression, SSL, or character‐set options.
Persistent handshake failures break application availability and can mask deeper version mismatches. Resolving the protocol option mismatch restores connectivity and avoids cascading outages in production environments.
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Enable --debug or --log_error_verbosity=3 on the server. The MySQL error log will include the exact option string.
No. The handshake aborts before any data is exchanged, so tables remain intact. It is purely a connection negotiation issue.
Ignoring it can hide performance hits and intermittent outages. Fixing the root capability mismatch improves stability.
Downgrading is risky and seldom necessary. Upgrading the client or correcting parameters is the safer path.
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