mysql_config: 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/mysql_config - from package: mysql55w
/usr/bin/mysql_config - from package: mysql

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

On Debian possible default full paths are:

/usr/bin/mysql_config - from package: libmysqlclient-dev

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

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