ORA-12518: TNS:listener could not hand off client connection


Sometimes You can get “ORA-12518: TNS:listener could not hand off client connection  ” error.


ORA-12518 TNS listener could not hand off client connection

Details of error are as follows.

ORA-12518: TNS:listener could not hand off client connection

Cause: The process of handing off a client connection to another process failed.

Action: Turn on listener tracing and re-execute the operation. Verify that the listener and database

instance are properly configured for direct handoff. If problem persists, call Oracle Support.
Edit /etc/systemd/system.conf file and Set DefaultTasksMax to ‘infinity’.

Or This error may be related with out of available Oracle processes parameter.


If processes parameters are insufficient, then you should increase the PROCESSES parameter as follows.


SQL> show parameter processes

------------------------------------ ----------- ------------------------------
aq_tm_processes integer 1
db_writer_processes integer 1
gcs_server_processes integer 0
global_txn_processes integer 1
job_queue_processes integer 1000
log_archive_max_processes integer 4
processes integer 1500
SQL> alter system set processes=2000 scope=spfile;

System altered.



Restart database after this operation.


If it is not related with processes parameter, then it may be related with dispatcher.

Firstly Shutdown the dispatcher and add new dispatchers as follows.

SQL> show parameter dispatchers
SQL> select name from v$dispatcher;
SQL> alter system shutdown immediate 'D001';
Add new dispatcher
SQL> alter system set DISPATCHERS = '(protocol=tcp)(dispatchers=4)';


Or you should check ‘max user processes’ etc. with ‘ulimit -a‘ command, and if it is insufficient, then increase it.


For windows environment.

set logging_listener_name=on in the listener.ora and reload the listener.

Or restart all Oracle services, it will be fine.


Do you want to learn more details about RMAN, then read the following articles.

RMAN Tutorial | Backup, Restore and Recovery Tutorials For Beginner Oracle DBA


About Mehmet Salih Deveci

I am Founder of SysDBASoft IT and IT Tutorial and Certified Expert about Oracle & SQL Server database, Goldengate, Exadata Machine, Oracle Database Appliance administrator with 10+years experience.I have OCA, OCP, OCE RAC Expert Certificates I have worked 100+ Banking, Insurance, Finance, Telco and etc. clients as a Consultant, Insource or Outsource.I have done 200+ Operations in this clients such as Exadata Installation & PoC & Migration & Upgrade, Oracle & SQL Server Database Upgrade, Oracle RAC Installation, SQL Server AlwaysOn Installation, Database Migration, Disaster Recovery, Backup Restore, Performance Tuning, Periodic Healthchecks.I have done 2000+ Table replication with Goldengate or SQL Server Replication tool for DWH Databases in many clients.If you need Oracle DBA, SQL Server DBA, APPS DBA,  Exadata, Goldengate, EBS Consultancy and Training you can send my email adress [email protected].-                                                                                                                                                                                                                                                 -Oracle DBA, SQL Server DBA, APPS DBA,  Exadata, Goldengate, EBS ve linux Danışmanlık ve Eğitim için  [email protected] a mail atabilirsiniz.

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