i8kfan: 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/i8kfan - from package: i8kutils

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

Error in other languages:
i8kfan: bevel nie gevind nie
i8kfan: comandă negăsită
i8kfan: comando não encontrado
i8kfan: commande introuvable
i8kfan: command not found
i8kfan: käsku ei ole
i8kfan: không tìm thấy lệnh
i8kfan: komanda nerasta
i8kfan: Kommando nicht gefunden.
i8kfan: kommandot finns inte
i8kfan: komut yok
i8kfan: nie znaleziono polecenia
i8kfan: níor aimsíodh an t-ordú
i8kfan: no se encontró la orden
i8kfan: no s'ha trobat l'ordre
i8kfan: opdracht niet gevonden
i8kfan: parancs nem található
i8kfan: perintah tidak ditemukan
i8kfan: príkaz nenájdený
i8kfan: příkaz nenalezen
i8kfan: команда не найдена
i8kfan: командата не е открита
i8kfan: 命令找不到
i8kfan: コマンドが見つかりません