How to work around error from opatch "LsInventorySession failed: OracleHomeInventory gets null oracleHomeInfo"

I recently had to investigate the patch level for an Oracle 10g database prior to an upgrade of an OAS application database.

This is the error I ran into:

myserver:asdb:ora10g>opatch lsinventory
Invoking OPatch 10.2.0.4.3

 
Inventory load failed... OPatch cannot load inventory for the given Oracle Home.
Possible causes are:
   Oracle Home dir. path does not exist in Central Inventory
   Oracle Home is a symbolic link
   Oracle Home inventory is corrupted
LsInventorySession failed: OracleHomeInventory gets null oracleHomeInfo

OPatch failed with error code 73

Fix this by running the attachHome.sh script in $ORACLE_HOME/oui/bin.
The Oracle Universal Installer allows you to set up an Inventory from scratch, or to register an existing ORACLE_HOME in an already existing Inventory.

myserver:asdb:ora10g>cd $ORACLE_HOME/oui/bin
/u01/oracle/product/ora10g/oui/bin
myserver:asdb:ora10g>./attachHome.sh
Starting Oracle Universal Installer...

No pre-requisite checks found in oraparam.ini, no system pre-requisite checks will be executed.
The inventory pointer is located at /etc/oraInst.loc
The inventory is located at /u01/oracle/oraInventory11g
'AttachHome' was successful.

Result:

myserver:asdb:ora10g>opatch lsinventory
Invoking OPatch 10.2.0.4.3

Oracle Interim Patch Installer version 10.2.0.4.3
Copyright (c) 2007, Oracle Corporation.  All rights reserved.


Oracle Home       : /u01/oracle/product/ora10g
Central Inventory : /u01/oracle/oraInventory11g
   from           : /etc/oraInst.loc
OPatch version    : 10.2.0.4.3
OUI version       : 10.2.0.4.0
OUI location      : /u01/oracle/product/ora10g/oui
Log file location : /u01/oracle/product/ora10g/cfgtoollogs/opatch/opatch2016-01-18_16-01-17PM.log

Lsinventory Output file location : /u01/oracle/product/ora10g/cfgtoollogs/opatch/lsinv/lsinventory2016-01-18_16-01-17PM.txt

--------------------------------------------------------------------------------
Installed Top-level Products (4):

Oracle Database 10g                                                  10.2.0.1.0
Oracle Database 10g Products                                         10.2.0.1.0
Oracle Database 10g Release 2 Patch Set 2                            10.2.0.3.0
Oracle Database 10g Release 2 Patch Set 3                            10.2.0.4.0
There are 4 products installed in this Oracle Home.


Interim patches (3) :

Patch  6979801      : applied on Fri Mar 06 10:47:02 CET 2009
   Created on 5 Feb 2009, 15:35:25 hrs PST8PDT
   Bugs fixed:
     6979801

Patch  6972843      : applied on Tue Oct 14 17:35:12 CEST 2008
   Created on 25 Jun 2008, 08:31:04 hrs UTC
   Bugs fixed:
     6972843

Patch  6823287      : applied on Tue Oct 14 17:26:32 CEST 2008
   Created on 30 Jun 2008, 10:27:42 hrs UTC
   Bugs fixed:
     6823287



--------------------------------------------------------------------------------

OPatch succeeded.

How to use dbms_metadata to generate DDL for constraints

set long 10000
set heading off
set trimspool on
set lines 300
set longchunksize 300
spool all_mycons.sql
exec dbms_metadata.set_Transform_param(dbms_metadata.session_transform,'SQLTERMINATOR',true);

select dbms_metadata.get_ddl('CONSTRAINT','SYS_C006257121','SCOTT')  FROM DUAL;

-- For Foreign key constraints, use the REF_CONSTRAINT constant:
select dbms_metadata.get_ddl('REF_CONSTRAINT','MYFOREIGNKEY_FK','SCOTT')  FROM DUAL;

How to use dbms_metadata to generate DDL for a trigger

set long 10000
set heading off
set trimspool on
set lines 300
set longchunksize 300
spool mytrigger.sql
exec dbms_metadata.set_Transform_param(dbms_metadata.session_transform,'SQLTERMINATOR',true);

select dbms_metadata.get_ddl('TRIGGER','MYTRIGGER','SCOTT')  FROM DUAL;

On a Linux system, what do the parameters shmall, shmmax and shmmni define?

shmall
* indicates the total amount of shared memory that the system can use at one time (measured in pages)

shmmax
* defines the maximum size in bytes of a single shared memory segment that a Linux process can allocate in its virtual address space, in bytes.
Oracle recommends that more than half of the physical memory is assigned to shmmax

shmmni
* defines the system wide maximum number of shared memory segments

How to join v$database with v$instance

Here is a useful query which displays basic information about the database, using v$database and v$instance.
Take the opportunity to calculate the uptime for the database by subtracting the value of startup_time from the current date.

col platform_name format a30
col open_mode format a20
col host_name format a20
col version format a10
col status format a20
col uptime format a30
col name format a10
set lines 300

SELECT D.NAME,D.PLATFORM_NAME,D.CREATED, D.OPEN_MODE,I.HOST_NAME,I.VERSION, I.ARCHIVER,I.STATUS,
   TO_DSINTERVAL( TO_CHAR(
                                    TO_TIMESTAMP(SYSDATE)-I.STARTUP_TIME
                                   )
                      ) "UPTIME", 
                      (SELECT ROUND(SUM(BYTES)/1024/1024/1024) FROM DBA_DATA_FILES) "DB size GB",  
                      ( SELECT ROUND(BYTES/1024/1024/1024) "mem GB" FROM V$SGAINFO WHERE NAME = 'Maximum SGA Size' ) "SGA max size GB"
  FROM V$DATABASE D INNER JOIN V$INSTANCE I 
  ON UPPER(D.NAME) = UPPER(I.INSTANCE_NAME);

Result may look like the following:

NAME	PLATFORM_NAME	CREATED	OPEN_MODE	HOST_NAME	VERSION	ARCHIVER	STATUS	UPTIME	DB size GB	SGA max size GB
proddb01	Linux x86 64-bit	10.12.2015 14:16:46	READ WRITE	prodserver01.mycompany.com	11.2.0.4.0	STARTED	OPEN	+00 13:59:55.000000	929	12

Generate "drop user" statement for schemas with and without objects

set lines 200
col owner format a20
col username format a30
col schema format a30


PROMPT ===================================================
PROMPT List of all schemas and number of Objects they own:
PROMPT ===================================================
select u.username "Schema", decode(count(*),1,0, count(*)) "Number of Objects"
from dba_users u left outer join dba_objects o
on u.username = o.owner
where u.username in (USER1','USER2','USER3')
group by u.username
order by username ASC;

set heading off
set trimspool on
set lines 200
set feedback off
spool drop_users.sql
select 'spool drop_users_SD4440.log' from dual;
select 'DROP USER ' || u.username
                    || DECODE(decode(count(*),1,0, count(*)),
                       '0',';'
                       , ' CASCADE;')
from dba_users u left outer join dba_objects o
on u.username = o.owner
where u.username in ('USER1','USER2','USER3')
group by u.username;
select 'exit' from dual;
exit

How to solve ORA-27102: out of memory on startup

You want to increase your SGA to a larger value, and you have taken care to increase the value of shmmax in the /etc/sysctl.conf file.

When starting up the database with increased values for sga_max_size and sga_target, you hit

SQL> startup
ORA-27102: out of memory
Linux-x86_64 Error: 28: No space left on device
Additional information: 1543503872
Additional information: 1

Solution:
Increase the value of shmall as well. Shmall indicates the total amount of shared memory that the system can use at one time (measured in pages).

To find the page size:

getconf PAGE_SIZE
4096

Make sure that the shmall is larger, not identical, than the setting of your SGA.
For example, if you want a 12G SGA, do not set shmall to 3145728 which would be the number of pages for 12G

Set it to a value larger instead, for example 3670016, which is the number of pages equivalent to 14G:

3670016*4096=15032385536
15032385536/1024/1024/1024 = 14G

As root, open /etc/sysctl.conf in an editor.
Search for the string kernel.shmall
Change the value
Save and exit.

Then, still as root, execute

sysctl -p

Check that the new settings are in place:

/sbin/sysctl -a | grep shm

The database should now be possible to open.