What is the longest (how much characters) for SSH password?
I like strong and long password but dont know the character limit.
There is no fixed maximum length. Your password is not stored, a "salted hash" of your password is stored, usually in the /etc/shadow file, which is always of a particular length. Even if your password is 50+ characters, the hashed representation of the password will be much smaller.
By all means use strong passwords, but passwords are meant to be easy to use and memorable - if you make it too long, you might end up needing to write it down, which would probably be a bigger security concern than a shorter password.
If the password is stored as DES or MD5 then only the first 8 characters are significant. SHA passwords have no such limit. See the