Reconstructing oratab from the cluster registry

At the Accenture Enkitec Group we have a couple of Exadata racks for Proof of Concepts (PoC), Performance validation, research and experimenting. This means the databases on the racks appear and vanish more than (should be) on an average customer Exadata rack (to be honest most people use a fixed few existing databases rather than creating and removing a database for every test).

Nevertheless we gotten in a situation where the /etc/oratab file was not in sync with the databases registered in the cluster registry. This situation can happen for a number reasons. For example, if you clone a database (RMAN duplicate), you end up with a cloned database (I sincerely hope), but this database needs to be manually registered in the cluster registry. This is the same with creating a standby database (for which one of the most used methods is to use the clone procedure with a couple of changes).

However, above reasons are quite obvious. But there is a another reason which is way less obvious: bug 17172091 (Oracle restart may update oratab incorrectly after a node reboot) can also cause your oratab to get out of sync with the databases/instances in the cluster registry. Additional information: Oracle versions confirmed being affected are 11.2.0.3 and 11.2.0.2. This is bug is reported to be fixed with Grid Infra PSU 11.2.0.3.9 and 11.2.0.4.2. (yes I am aware of the inconsistency between versions affected and fixed versions, this is from the Oracle bug information available; thanks to Tanel Põder for finding this bug).

In order to recreate the oratab, you need to go through the cluster registry information, and compare it with your oratab. Especially if you’ve got a lot of databases, and/or single instance databases in different nodes, this can be quite some work. To relieve work for that situation, I created a little shell script to parse the cluster registry database information and get the db_unique_name (which is what the first field actually is in the oratab file, thanks to Randy Johnson) and oracle home path information and output this in “oratab format” (db_name:oracle home path:N). Needless to say, this script just outputs it to STDOUT. If you want to use this information, redirect it to a file, or copy and past it in oratab yourself.

for resource in $(crsctl status resource -w "((TYPE = ora.database.type) AND (LAST_SERVER = $(hostname -s)))" | grep ^NAME | sed 's/.*=//'); do 
	full_resource=$(crsctl status resource -w "((NAME = $resource) AND (LAST_SERVER = $(hostname -s)))" -f)
	db_name=$(echo "$full_resource" | grep ^DB_UNIQUE_NAME | awk -F= '{ print $2 }')
	ora_home=$(echo "$full_resource" | grep ^ORACLE_HOME= | awk -F= '{ print $2 }')
	printf "%s:%s:N\n" $db_name $ora_home 
done

Note: changed db_unique_name to db_name in the “oratab format” description, which is how the format truly looks like.