unknown variable 'pid-file=/run/mysqld/mysqld.pid' when setting 50-server.cnf

Question

I am modifying /etc/mysql/mariadb.conf.d/50-server.cnf

When I add the following code, i get the error unknown variable 'pid-file=/run/mysqld/mysqld.pid'

[mysql]
default-character-set = utf8mb4

I am adding the mysql tag as well as it is not in the file, but I don't understand why this line is effecting the pid variable which seems to be defined in the mysql conf file.

Any ideas?

full contents of 50-server.cnf

[server]

[mysqld]
innodb-file-format=barracuda
innodb-file-per-table=1
innodb-large-prefix=1
character-set-client-handshake = FALSE
character-set-server = utf8mb4
collation-server = utf8mb4_unicode_ci

[mysql] 
default-character-set = utf8mb4

# * Basic Settings
#
user                    = mysql
pid-file                = /run/mysqld/mysqld.pid
socket                  = /run/mysqld/mysqld.sock
#port                   = 3306
basedir                 = /usr
datadir                 = /var/lib/mysql
tmpdir                  = /tmp
lc-messages-dir         = /usr/share/mysql
#skip-external-locking

bind-address            = 127.0.0.1
query_cache_size        = 16M

log_error = /var/log/mysql/error.log
expire_logs_days        = 10
character-set-server  = utf8mb4
collation-server      = utf8mb4_general_ci

[embedded]

[mariadb]

[mariadb-10.3]

Answer 1

To formally put this as an answer, the square brackets denote sections of the config and you cut the [mysqld] section in half with your inserted [mysql] section. This has the affect of putting the pid-file setting under [mysql] rather than [mysqld]. Judging my the error, [mysql] does not have a a pid-file setting.

Either add your [mysql] settings at the top or bottom of the file and you should be set. Alternatively, put them into a sibling file 50-server.cnf called 51-client.cnf so you can easily find them in the future (the number in the file name is load order and the name is arbitrary).