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Don Burleson Blog 







ORA-12542: TNS:address already in use tips

Oracle Database Tips by Donald BurlesonAugust 24,  2015

Question:  I am able to make 42 and more connections of my Application Users within 8 terminals.  When 9th terminal connects I'm getting the ORA-12542 error:

Error ORA-12542: TNS:address already in use

What is the solution to the ORA-12542 error?


The docs note this on the ORA-12542 error:

ORA-12542: TNS:address already in use

Cause: Specified listener address is already being used.

Action: Start your listener with a unique address.

Fixing the ORA-12542 on UNIX/Linux

In UNIX, the ORA-12542 error is an easy fix, just re-set the listener to run on a different port or add to the queue size for the listener in your listener.ora file. 


Fixing the ORA-12542 on Windows

The error "ORA-12542: TNS:address already in use" is rare on UNIX but very common on Windows crapware and /net platforms, and this may be a bug.  See MOSC Note:252614.1,  and search for bugs relating to ORA-12542.  It may have to do with a memory leak. 

On Windows, user SJH suggests this solution for the ORA-12542 error:

[The ORA-12542 TNS address in use error] is caused due to the fact that the free ports in the windows client has been exhausted and it is trying to make use of a port which is in TIME_WAIT state which gives the error TNS-12542: Address already in use.

There are 2 solutions available:

1.) Increase the free port range:
Start Registry Editor (Regedt32.exe).

Locate the following key in the registry:


On the Edit menu, click Add Value, and then add the following registry value:

Value Name: MaxUserPort Data Type: REG_DWORD Value: 65534

Valid Range: 5000-65534 (decimal) Default: 0x1388 (5000 decimal)

Description: This parameter controls the maximum port number used when an application requests any available user port from the system. Normally, ephemeral (that is, short-lived) ports are allocated between the values of 1024 and 5000 inclusive.

2.) Decrease the value for TIME_WAIT state:
TcpTimedWaitDelay (new in Windows NT versions 3.51 SP5 and later)
Key: Tcpip\Parameters
Value Type: REG_DWORD - Time in seconds
Valid Range: 30-300 (decimal)
Default: 0xF0 (240 decimal)



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