Can't connect to DB2 instance: SQL1031N The database directory cannot be found on the indicated file system. SQLSTATE=58031

I have been having nothing but trouble with DB2, it works then it doesn't then it works again, then it fails again. My current problem is trying to connect to an instance I created. I'm logged in as my instance user; db2inst1.

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When I use to command:

connect to db2inst1

I'm presented with:

SQL1031N  The database directory cannot be found on the indicated file system. 
SQLSTATE=58031

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db2start and db2stop both work.

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db2 list db directory

shows:

     System Database Directory

 Number of entries in the directory = 1

     Database 1 entry:
     Database alias                       = DB2INST1
     Database name                        = DB2INST1
     Local database directory             = /home/db2inst1
     Database release level               = 10.00
     Comment                              =
     Directory entry type                 = Indirect
     Catalog database partition number    = -1
     Alternate server hostname            =
     Alternate server port number         =

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echo $DB2DIR shows /opt/ibm/db2/V10.5

The harddrive I'm using uses ext4. I have tried re-cataloging the instance.

I have no idea what the problem is, I've followed many tutorials step for step and everything seemed to work fine for them.

Could anyone please shine a light?