Where is my mysqld.conf file located?

I am trying to do this tutorial, and the first step is to modify the mysqld.conf file. Although when I run the command to edit this file it says this: [ Directory '/etc/mysql/mysql.conf.d' does not exist ]. In my /etc/mysql directory when I run ls I can’t find this file either:

root@...:/etc/mysql# ls

conf.d      debian-start  mariadb.conf.d  my.cnf.fallback
debian.cnf  mariadb.cnf   my.cnf

which os you are using?

configuration file is my.cnf that is in your massage