mysqld_multi: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/bin/mysqld_multi - from package: mysql55w-server
/usr/bin/mysqld_multi - from package: mysql-server

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/mysqld_multi - from package: mariadb-server-10.0
/usr/bin/mysqld_multi - from package: mysql-server-5.5

You may install the required package with command apt-get install {package}

Error in other languages:
mysqld_multi: bevel nie gevind nie
mysqld_multi: comandă negăsită
mysqld_multi: comando não encontrado
mysqld_multi: commande introuvable
mysqld_multi: command not found
mysqld_multi: käsku ei ole
mysqld_multi: không tìm thấy lệnh
mysqld_multi: komanda nerasta
mysqld_multi: Kommando nicht gefunden.
mysqld_multi: kommandot finns inte
mysqld_multi: komut yok
mysqld_multi: nie znaleziono polecenia
mysqld_multi: níor aimsíodh an t-ordú
mysqld_multi: no se encontró la orden
mysqld_multi: no s'ha trobat l'ordre
mysqld_multi: opdracht niet gevonden
mysqld_multi: parancs nem található
mysqld_multi: perintah tidak ditemukan
mysqld_multi: príkaz nenájdený
mysqld_multi: příkaz nenalezen
mysqld_multi: команда не найдена
mysqld_multi: командата не е открита
mysqld_multi: 命令找不到
mysqld_multi: コマンドが見つかりません