Your Oracle Database is Down!

A developer comes to you and asks you, " is your Dev. database down?" I cannot connect to the development database, can you please check? I am glad he didn't say production database. Below, I have compiled the checklist to verify why the database might not be accepting connections. Each DBA has their style to tackle this issue. This article focuses on talks to novice dba as why it is not accepting any connections.  Before, you jump into troubleshooting the issue, let's take a few min and think what could have caused this?What are the possibilities?See all the possibilities below:

Possibilities:

1. The Server that is hosting the DB might be down.
2. The listener could be down
3. The database might be down
4. User Error- ( may have used wrong log in credentials, local TNS file corruption, other, etc....)

Troubleshooting Steps:

1. Check the Server where the Oracle is running (ping the host from the network)
2. Check the Oracle Process (ps -ef | egrep pmon)
3. Check the Listener Process (ps -ef | egrep lsn)
4. Check the Listener Status  ( lsnctrl status)
5.  Log into SQL Plus (sqlplus / as sysdba)
6.  Check if the database is Open, and in READ &Write mode  ( select * from v$database; or select * from v$instance)
7.  Check if you can write to a table- verify the alert log

By now your database Instance should be up and working or if not, you know where the problem lies. Please feel  free to add to this list if you have different experience or wants to know more on it.