All Oracle errors
TNS-12560net

TNS protocol adapter error

TNS-12560: TNS:protocol adapter error

Why it happens

The listener or client could not initialise a protocol adapter, often after an OS or network change, an invalid listener.ora parameter, or a port conflict.

How to fix it

Check the listener log for the accompanying OSN- error, validate listener.ora syntax, confirm the hostname resolves, and restart the listener. On Windows, verify the service account can open the configured port.

A note on TNS-12560

This entry is part of a hand-curated set of ORA-, FRM-, REP- and TNS- codes that actually turn up in production Oracle estates — SQL*Plus, APEX, 19c/21c, ODP.NET apps, Oracle Forms 6i/12c and Reports included. The message text above is the canonical wording; the cause and fix are written in plain language so a developer or DBA can act without digging through pages of Oracle reference docs first.

Codes outside this list of 44 are far less common. If you hit one, the official Oracle error reference and your instance's alert or listener log remain the authoritative source.

Related net errors

ORA-03113 · End-of-file on communication channel ORA-03114 · Not connected to ORACLE ORA-12154 · TNS cannot resolve connect identifier

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