Below are the steps I've taken to finally migrate my self hosted Known site from MySQL to PostgreSQL.
Currently the website install routine only supports MySQL so there is no need to go to either the /warmup or /begin folders on your site. You need to build that database manually.
createdb -T template1 -O withknown withknown
psql -f /schema/postgres/postgres.sql withknown
To migrate the data from MySQL to PostgreSQL I use the mysql2postgresql tool from Mihail Shumilov
mysqldump --xml -u root withknown > withknown.xml
php convertor.php -i withknown.xml -o withknown.sql
Edit the file withknown.sql and remove all the DROP, CREATE, ALTER lines so you are left with only the INSERT lines, which hold the actual site data. (perhaps there is a option in mysqldump to do this directly)
To get rid of the over escaping from MySQL run the below sed line.
cat withknown.sql | sed -e 's/\\\\/\\/g' > withknown-final.sql
As last phase import the data in PostgreSQL
sql -U withknown -f withknown-final.sql withknown
Make sure you update the config.ini and change the connection info
database = 'Postgres'
dbname = 'withknown'
dbpass = 'XXX'
dbuser = 'withknown'
dbhost = 'localhost'