Cannot connect to the VMware vCenter Server Appliance 5.x

VMware vCenter Server

Symptoms:

You cannot connect to the VMware vCenter Server Appliance (VCSA) using the vSphere Client.
In the VCSA console, you see the error:

waiting for the embedded database to start up.............. failed
In the /var/log/vmware/vpx/vpxd.log file,you see entries similar to:

[VpxdVdb::SetDBType] Logging in to DSN: VMware VirtualCenter with username vc
[VpxdVdb::SetDBType] Logging in to DSN: VMware VirtualCenter with username vc
[VpxdVdb::SetDBType] Logging in to DSN: VMware VirtualCenter with username vc
[VpxdVdb::SetDBType] Logging in to DSN: VMware VirtualCenter with username vc
[VpxdVdb::SetDBType] Logging in to DSN: VMware VirtualCenter with username vc
[VpxdVdb::SetDBType] Logging in to DSN: VMware VirtualCenter with username vc
[VpxdVdb::SetDBType] Failed to connect to database: ODBC error: (08001) - [unixODBC]could not connect to server: Connection refused
--> Is the server running on host "127.0.0.1" and accepting
--> . Retry attempt: 193 ...
--> TCP/IP connections on port 5432?

Note: The preceding log excerpts are only examples. Date, time, and environmental variables may vary depending on your environment.

VMware vCenter Server Appliance 5.5.x
VMware vCenter Server Appliance 5.1.x
VMware vCenter Server Appliance 5.0.x

This issue occurs if the vCenter Server Appliance has lost its ODBC configuration and is unable to start the embedded DB2 database.

Note: This issue can also be caused due to an out of space issue. For more information, see vCenter Server Appliance with embedded vPostgres database crashes due to full database partition (2058273).

To resolve this issue, reconfigure the ODBC connection.

To reconfigure the ODBC connection:

Connect to the vCenter Server Appliance through SSH as the root user. The default password is vmware.

Note: To enable SSH on the vCenter Server Appliance 5.x, see the Enable or Disable SSH Administrator Login on the VMware vCenter Server Appliance section in the vCenter Server and Host Management Guide.
Run this command to stop the vpxd service:

service vmware-vpxd stop
Run this command:

/usr/sbin/vpxd_odbcconfig

You see output similar to:

VMware vCenter Server Appliance ODBC Configuration

Choose a database to use with VMware vCenter Server

1) oracle
2) embedded
Enter 2.

You see output similar to:

Configuring ODBC for embedded
Operation was successful.
Database already populated with version VirtualCenter Database 5.0
Reinitialize database? (WARNING: WILL DELETE ALL RECORDS) [y(es)|N(O)]: OK, preserving the database. (select No to preserve the database)
Restart vCenter Server now to activate the database changes [y/N]:y
Successfully restarted vCenter Server