smartctl: 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/sbin/smartctl - from package: smartmontools

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

On Debian possible default full paths are:

/usr/sbin/smartctl - from package: smartmontools

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

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