This is what I have in the folder
root@d7:/etc/mysql# ls -ail
total 48
1055141 drwxr-xr-x 4 root root 4096 Apr 6 11:09 .
1044481 drwxr-xr-x 141 root root 12288 Apr 6 11:04 ..
1055175 drwxr-xr-x 2 root root 4096 Apr 6 11:03 conf.d
1044616 -rw------- 1 root root 277 Mar 26 11:57 debian.cnf
1045134 -rw------- 1 root root 333 Feb 23 09:07 debian_old_config.fsDTDb
1055184 -rwxr-xr-x 1 root root 1312 Feb 3 04:34 debian-start
1055178 -rw-r--r-- 1 root root 744 Feb 9 20:21 mariadb.cnf
1055147 drwxr-xr-x 2 root root 4096 Mar 24 10:03 mariadb.conf.d
1055143 -rw-r--r-- 1 root root 3540 Apr 6 11:09 my.cnf
1055174 -rw-r--r-- 1 root root 3506 Feb 16 11:49 my.cnf.dpkg-old
May be I have to rename mariadb.cnf to my.cnf?
What I found is
two folder with config-add options.
conf.d
mariadb.conf.d
root@d7:/etc/mysql# ll -lailR
.:
total 48
1055141 drwxr-xr-x 4 root root 4096 Apr 6 12:10 .
1044481 drwxr-xr-x 141 root root 12288 Apr 6 11:04 ..
1055175 drwxr-xr-x 2 root root 4096 Apr 6 11:03 conf.d
1044616 -rw------- 1 root root 277 Mar 26 11:57 debian.cnf
1045134 -rw------- 1 root root 333 Feb 23 09:07 debian_old_config.fsDTDb
1055184 -rwxr-xr-x 1 root root 1312 Feb 3 04:34 debian-start
1055178 -rw-r--r-- 1 root root 744 Feb 9 20:21 mariadb.cnf
1055147 drwxr-xr-x 2 root root 4096 Mar 24 10:03 mariadb.conf.d
1055143 -rw-r--r-- 1 root root 3540 Apr 6 11:09 my.cnf
1055174 -rw-r--r-- 1 root root 3506 Feb 16 11:49 my.cnf.dpkg-old
./conf.d:
total 20
1055175 drwxr-xr-x 2 root root 4096 Apr 6 11:03 .
1055141 drwxr-xr-x 4 root root 4096 Apr 6 12:10 ..
1055176 -rw-r--r-- 1 root root 0 Nov 25 19:01 .keepme
1055177 -rw-r--r-- 1 root root 435 Feb 3 04:34 mariadb.cnf
1055186 -rw-r--r-- 1 root root 21 Feb 3 04:33 mysqld_safe_syslog.cnf
1055185 -rw-r--r-- 1 root root 285 Jan 25 16:21 tokudb.cnf
./mariadb.conf.d:
total 20
1055147 drwxr-xr-x 2 root root 4096 Mar 24 10:03 .
1055141 drwxr-xr-x 4 root root 4096 Apr 6 12:10 ..
1055173 -rw-r--r-- 1 root root 111 Feb 8 13:32 client.cnf
1055166 -rw-r--r-- 1 root root 2715 Feb 8 13:32 mysqld.cnf
1055148 -rw-r--r-- 1 root root 306 Feb 8 13:32 mysqld_safe.cnf