ORA-00020: maximum number of processes (5000) exceeded

Symptom

After an ORA-00020 "maximum number of processes (%s) exceeded" occurs ... no new connections (even SYSDBA or SYSOPER) may be made to the instance.

Solution

An ORA-20 "maximum number of processes (%s) exceeded" occurs when the number of OS processes for the instance exceeds the PROCESSES parameter 

There are a couple of 'workarounds' for this issue

WORKAROUNDS:

* UNIX: kill -9 one or more of the client connections 
* WINDOWS : using ORAKILL ... kill one or more of the client connections 
* Use an existing connection with sufficient privileges (if one is logged on) to view V$SESSION / V$PROCESS and 
         alter system kill session 'SID, SERAL#';

In my case I don't have any active sessions with sufficient privileges

As of 10.1.x, there is a new option with SQL*Plus to allow access to an instance to generate traces.

You can shut abort and then restart your database, instead of rebooting your server.

This is the ultimate chance before reboot. Before doing this, consider disconnecting or killing some user session to get a regular sqlplus / as sysdba.