efax-0.9a: 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/efax-0.9a - from package: efax-gtk

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

Error in other languages:
efax-0.9a: bevel nie gevind nie
efax-0.9a: comandă negăsită
efax-0.9a: comando não encontrado
efax-0.9a: commande introuvable
efax-0.9a: command not found
efax-0.9a: käsku ei ole
efax-0.9a: không tìm thấy lệnh
efax-0.9a: komanda nerasta
efax-0.9a: Kommando nicht gefunden.
efax-0.9a: kommandot finns inte
efax-0.9a: komut yok
efax-0.9a: nie znaleziono polecenia
efax-0.9a: níor aimsíodh an t-ordú
efax-0.9a: no se encontró la orden
efax-0.9a: no s'ha trobat l'ordre
efax-0.9a: opdracht niet gevonden
efax-0.9a: parancs nem található
efax-0.9a: perintah tidak ditemukan
efax-0.9a: príkaz nenájdený
efax-0.9a: příkaz nenalezen
efax-0.9a: команда не найдена
efax-0.9a: командата не е открита
efax-0.9a: 命令找不到
efax-0.9a: コマンドが見つかりません