gfax: 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/gfax - from package: gfax

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

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