gfan: 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/gfan - from package: gfan

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

On Debian possible default full paths are:

/usr/bin/gfan - from package: gfan

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

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