Postgresql – pg_basebackup: could not get WAL end position from server

That Postgres configuration looks right

CentOS by default sets the user directory mode to 700 so check if that's actually the case and if you can touch that file using su as the root user

su - postgres -c "touch /home/myusername/backup/testtouch"

If that does work then try to use verbose logging in postgres and check the postgres log for further errors.

The unintended upgrade is Amazon's packaging fault. The other Linux distributions normally don't break PostgreSQL when upgrading.

To get out of this mess, see this entry in their FAQ:

What steps do I take to upgrade from PostgreSQL 9.1 to 9.2?

PostgreSQL 9.2 offers important new features and performance improvements and it has been included in the Amazon Linux AMI 2012.09 release based on customer requests.

After upgrading PostgreSQL from 9.1 to 9.2, the database service will no longer start. This happens because the 9.1 version of the database format is not immediately usable with the 9.2 server. We have provided the postgresql-upgrade package as an automatic install alongside the latest release of postgresql 9.2. This allows you to perform an in-place upgrade on your database using service postgresql upgrade.

Behind the scenes, this runs pg_upgrade to migrate your database to the new format. Note that the upgrade will reset configuration files such as pg_hba.conf to a clean state. Your old configuration files are stored in /var/lib/pgsql9/data-old, and can be copied over the default files in /var/lib/pgsql9/data after your review.

Once the upgrade is finished and the configuration files are restored, the service should start normally.