mysqltuner: 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/mysqltuner - from package: mysqltuner

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

On Debian possible default full paths are:

/usr/bin/mysqltuner - from package: mysqltuner

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

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