ssh script returns 255 error

Question

In my code I have the following to run a remote script.

ssh root@host.domain.com \"sh /home/user/backup_mysql.sh\"

For some reason it keeps

Answer 1

This error will also occur when using pdsh to hosts which are not contained in your "known_hosts" file.

I was able to correct this by SSH'ing into each host manually and accepting the question "Do you want to add this to known hosts".