It was installed, but not upgraded. After reinstalling krb5-plugin-kdb-ldap the error of the unknown symbol 'kdb_function_table' disappeared, but krb ist still broken and not starting. krb logs says: krb5kdc: Cannot bind to LDAP server 'ldapi:///' as 'cn=Administrator,dc=xxx,dc=de': Invalid credentials - while initializing database for realm XXX.DE