Since I want to share an existing DB with the later slave-site (ONE DB FOR MASTER AND SLAVE SITES), I have a problem.

You wrote that the "jos_"-Prefix (in my existing DB) will be overwrite, when installing new slave sites.

"
Single database to store the information of all the websites (master
and slave sites). In this case, ‘jos_’ table prefix is forbidden."


Does this mean, that I have to change all the "jos_"-Prefixes in the entries of my existing DB in order to run only ONE DB for all sites?


Thanks.

Bests Mark

Concerning "jos_" we didn't say "will be" overwiten but "might be" overwriten if
you don't take care about the table prefix.
"jos_" is the default table prefix used by Joomla and if you forget to replace the table prefix when creating a slave site, you might perhaps overwirte your master website.
This is the reason why we do not recommend to never use "jos_" as table prefix.

If you are an expert and never make any mistake, you can continue to use "jos_" as table prefix. But at your own risk. If you forget only once to enter a specific table prefix, you will overwrite the "jos_" table prefix with a fresh slave site and therefore will destroy your master website.

You don't have to delete "jos_" table prefix if it already exists.
We just recommend to use another DB to reduce the risk to overwitie it.

I hope this is more clear

The different scenario are explained in the user manual.