gfan_substitute: 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/gfan_substitute - from package: gfan

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

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