All Oracle errors
TNS-12154net

Could not resolve connect identifier

TNS-12154: TNS:could not resolve the connect identifier specified

Why it happens

The client could not map the alias to a connect descriptor: a missing tnsnames.ora entry, wrong TNS_ADMIN, or a typo in the alias.

How to fix it

Run tnsping <alias> from the same client, check TNS_ADMIN and tnsnames.ora, and escape special characters. For EZConnect, use host:port/service instead of an alias.

A note on TNS-12154

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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