hpifan: 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/hpifan - from package: openhpi32
/usr/bin/hpifan - from package: openhpi

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

On Debian possible default full paths are:

/usr/bin/hpifan - from package: openhpi-clients

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

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