Why do I keep getting ORA-01033: ORACLE initialization or shutdown in progress when my database is open? (12c) I'm running Oracle on a Windows server (maybe that is why it is so buggy?). It was working fine for a bit, but lately I've been having an issue.  I keep getting the ORA-01033: ORACLE initialization or shutdown in progress error.  

If go into the server and run SQLPlus and check the v$instance table it says my instance is open.  I'm able to switch to my pluggable database.  v$database shows  that my database is read/write.  

I have a linked server set up from my MS SQL Server and it will work for awhile and then return ORA-01033.  So, maybe it's just SQL Server I say and try SQL Developer.  I get the same error!  Just for kicks I create a new connection on SQL Developer, and it works.  For a little while.  Then I get this: 

I only have ~30 GB of freespace on the drive where Oracle is loaded.  Could that be causing the issue?  If I reboot the server it works.  For a little while.  Basically, it seems to work until I start hammering on it and pulling a lot of data out.
I can't tell you why this happens, but I get such errors regularly with the pluggable database. What I do as a quick fix is I connect using sqlplus "/ as sysdba", then I run the following code for that specific database:

alter pluggable database orclpdb open;


Or the following for all databases:

alter pluggable database all open;


And I stop getting the errors for a while... until the next time it happens. :)
At least I have a quick procedure as a fix.