How to check the password file version

oracle@oric01.oric.no:[PRODDB01]# orapwd describe file=/u01/oracle/product/12201/dbs/orapwPRODDB01
Password file Description : format=LEGACY

If you try to create the password file with a password that is too simple, you may see this error from orapwd:

OPW-00029: Password complexity failed for SYS user : Password must contain at least 8 characters

The format is set to 12.2 by default, and from the orapwd help text there doesn't seem to be anything lower than this.
If you for some reason need to keep an old password which is too simple for today's default settings, you can create a "legacy" password by using the format "legacy". This is not documented in the help text:

orapwd file=u01/oracle/product/12201/dbs/orapwPRODDB01 format=legacy force=Y

Enter password for SYS:

How to perform a full export and import of an entire database in PostgreSQL

Export the database "db01" from your source postgres server:

pg_dump db01 -v -Fc >db01.dmp

The -v means "verbose" and -Fc means "custom format" (as opposed to "directory format", which would be indicated by -Fd)

Import the database "db01" in your destination postgres server

First, transfer the directory db01.dmp file from the source server to the target server using scp.

pg_restore -v -d db01 -1 db01.dmp

The -1 option means "all or nothing"; either the entire operation succeed, or nothing is done.

If the database doesn't exist, you need to connect to another database in the cluster first:

pg_restore -v -C -d postgres /exports/full_db_export.dmp

Export the database "db01" using the directory format:

pg_dump -Fd db01 -f /exports/full_db01 -v

This will create the directory /exports/full_db01 which contains all the files necessary for restore. The -v means "verbose" and -Fd means "directory format"

Import the database "db01":

Again, transfer the needed files, this time the entire directory /exports/full_db01 from the source server to the target server using scp.
Then import the database, either by recreating the database indicated by the -C option:

pg_restore /exports/full_db01 -C -c -d postgres -j 2 -v

or by importing the objects into an existing database, in my case "db02":

pg_restore /exports/full_db01 -c -d db02 -j 2 -v

The -C option means "create database".

The -d postgres option indicates the database to which the pg_dump utility makes an initial connection

The -c option means "drop the database objects before creating"

-j is the number of jobs started in parallel

The official documentation for the pg_dump utility can be found here
here

what is the difference between DBA_AUDIT_TRAIL and DBA_COMMON_AUDIT_TRAIL?

The difference between these views is that DBA_COMMON_AUDIT_TRAIL contains information from both standard and fine-grained auditing, while DBA_AUDIT_TRAIL only contains information from standard auditing.

DBA_AUDIT_TRAIL displays all standard audit trail entries. 

This view is populated only in an Oracle Database where unified auditing is not enabled. 

The SQL_BIND and SQL_TEXT columns are only populated if the AUDIT_TRAIL initialization parameter is set to 'db, extended'. 

DBA_COMMON_AUDIT_TRAIL displays 

• All standard audit trail entries 
• Fine-grained audit trail entries 
• Mandatory audit trail entries 
• SYS audit records written in XML format 

The SQL_BIND and SQL_TEXT columns are only populated if the AUDIT_TRAIL initialization parameter is set to 'db, extended' or 'xml, extended' or if the AUDIT_SYS_OPERATIONS initialization parameter is set to TRUE.

How to set parallelism for a data guard recovery process

If you need to manually set the apply-process DOP (Degree of Parallelism), you can do this by setting the property ApplyParallel=num where num is the number of parallel processes. 

In my setup, I have three databases: 

•  A primary database (hdal) 
• A physical standby database (hdal_stb) which serves as a "cascading" database 
• A terminal standby database (hdal_tstb) which receives redo from the cascading standby database  

Logged in on any one of the participating servers of your data guard configuration, start dgmgrl: 

dgmgrl / as sysdba
Connected to "hdal_stb"
Connected as SYSDBA.
DGMGRL> show configuration;

Configuration - DGConfig1

  Protection Mode: MaxPerformance
  Members:
  hdal      - Primary database
    hdal_stb  - Physical standby database
      hdal_tstb - Physical standby database (receiving current redo)

DGMGRL> edit database 'hdal_stb' set property ApplyParallel=4;

In the database's alert log, we can se that Oracle is cancelling the ongoing recovery process:

ALTER DATABASE RECOVER MANAGED STANDBY DATABASE CANCEL
2020-08-10T09:26:24.249847+02:00
MRP0: Background Media Recovery cancelled with status 16037
Managed Standby Recovery not using Real Time Apply
Recovery interrupted!
Recovered data files to a consistent state at change 27754456
2020-08-10T09:26:24.510262+02:00
ORA-16037: user requested cancel of managed recovery operation
2020-08-10T09:26:24.617519+02:00
MRP0: Background Media Recovery process shutdown (hdal)
2020-08-10T09:26:25.250904+02:00
Managed Standby Recovery Canceled (hdal)

And then starting it again:

Completed: ALTER DATABASE RECOVER MANAGED STANDBY DATABASE CANCEL
ALTER DATABASE RECOVER MANAGED STANDBY DATABASE DISCONNECT PARALLEL 4 NODELAY
2020-08-10T09:26:25.284547+02:00
Attempt to start background Managed Standby Recovery process (hdal)
Starting background process MRP0
2020-08-10T09:26:25.306150+02:00
MRP0 started with pid=77, OS id=115854
2020-08-10T09:26:25.311038+02:00
MRP0: Background Managed Standby Recovery process started (hdal)
2020-08-10T09:26:30.339894+02:00
 Started logmerger process
2020-08-10T09:26:30.378497+02:00
Managed Standby Recovery starting Real Time Apply
2020-08-10T09:26:30.515607+02:00
Parallel Media Recovery started with 4 slaves
2020-08-10T09:26:30.741846+02:00
Media Recovery Waiting for thread 1 sequence 8299 (in transit)

Verify the new setting by looking at the properties (output truncated for brevity):

DGMGRL> show database verbose hdal_stb

Database - hdal_stb

  Role:               PHYSICAL STANDBY
  Intended State:     APPLY-ON
  Transport Lag:      0 seconds (computed 1 second ago)
  Apply Lag:          0 seconds (computed 1 second ago)
  Average Apply Rate: 0 Byte/s
  Active Apply Rate:  0 Byte/s
  Maximum Apply Rate: 0 Byte/s
  Real Time Query:    OFF
  Instance(s):
    hdal

  Properties:
    DGConnectIdentifier             = 'hdal_stb'
    LogXptMode                      = 'ASYNC'
    ApplyParallel                   = '4'

The change will be propagated to the other members of the data guard configuration. The data guard broker logfile, located in $ORACLE_BASE/diag/rdbms/$UNIQUE_NAME/$ORACLE_SID/trace, shows:

08/10/2020 09:26:24
Forwarding EDIT_RES_PROP operation to member hdal for processing
08/10/2020 09:26:31
Updated broker configuration file available, loading from "$ORACLE_HOME/dbs/dr2hdal_stb.dat"
08/10/2020 09:42:35
Forwarding MON_PROPERTY operation to member hdal_tstb for processing

The cascading database hdal_tstb simply confirms that the broker configuration has been updated:

08/10/2020 09:26:31
Updated broker configuration file available, loading from "$ORACLE_HOME/dbs/dr2hdal_tstb.dat"

The primary database is also verifying the change, although a bit more detailed:

08/10/2020 09:26:24
EDIT DATABASE hdal_stb SET PROPERTY applyparallel = 4
08/10/2020 09:26:31
EDIT INSTANCE hdal ON DATABASE hdal_stb SET PROPERTY applyparallel = 4 completed successfully

Documentation for dgmgrl version 19c can be found here

What constitute "mandatory auditing" under Unified Auditing?

• Activities from administrative users such as SYSDBA, SYSBACKUP, and SYSKM. 
•  The following audit-related activities are mandatorily audited:

CREATE AUDIT POLICY	AUDIT	EXECUTE of the DBMS_FGA PL/SQL package
ALTER AUDIT POLICY	NOAUDIT	EXECUTE of the DBMS_AUDIT_MGMT PL/SQL package
DROP AUDIT POLICY	Access to sensitive columns in the optimizer dictionary tables.	ALTER TABLE attempts on the AUDSYS audit trail table
Top level statements by the administrative users SYS, SYSDBA, SYSOPER, SYSASM, SYSBACKUP, SYSDG, and SYSKM, until the database opens	All user-issued DML statements on the SYS.AUD$ and SYS.FGA_LOG$ dictionary tables	Any attempts to modify the data or metadata of the unified audit internal table. SELECT statements on this table are not audited by default or mandatorily.
All configuration changes that are made to Oracle Database Vault

The audit information can be found in the view UNIFIED_AUDIT_TRAIL.
Documentation for Mandatory Unified Auditing in Oracle 12.2 can be found here

How to find offending process when getting error umount.nfs: /data1: device is busy

As root, use lsof ("list open files"):

[root@myserver /home/oracle]# lsof | grep '/data1'
extract    14041        oracle   25r      REG               0,23      2896 1235955379 /data1/goldengate/dirdat/et000000127 (storage1:/Oracle/myserver/data1)

You will see a list of processes. Terminate these with the kill-command:

kill 13859 14041 

After this is done, you can unmount the nfs file system:

 umount -f /data1

How to connect to and start a specific database using dgmgrl

The data guard broker allows you to connect to any of the participating members of the configuration:

oracle@myserver:[hdal]# dgmgrl / as sysdba
DGMGRL for Linux: Release 12.2.0.1.0 - Production on Fri Jul 31 10:44:47 2020

Copyright (c) 1982, 2017, Oracle and/or its affiliates.  All rights reserved.

Welcome to DGMGRL, type "help" for information.
Connected to "hdal"
Connected as SYSDBA.
DGMGRL> show configuration

Configuration - DGConfig1

  Protection Mode: MaxPerformance
  Members:
  hdal      - Primary database
    hdal_stb  - Physical standby database
      hdal_tstb - Physical standby database (receiving current redo)

Fast-Start Failover: DISABLED

Configuration Status:
SUCCESS   (status updated 51 seconds ago)

DGMGRL> connect sys@hdal_stb as sysdba
Password:
Connected to "hdal_stb"
Connected as SYSDBA.

Note that the password files must be identical for all members of the configuration.
You can startup and shutdown individual members of your configuration without leaving the data guard broker interface, for example:

DGMGRL> startup mount
ORACLE instance started.
Database mounted.

Documentation on how to use Oracle 12.2 version of dgmgrl is found here