mrtg-sensors: 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 Debian possible default full paths are:

/usr/bin/mrtg-sensors - from package: mrtgutils-sensors

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

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