efax: 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/efax - from package: efax

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

On Debian possible default full paths are:

/usr/bin/efax - from package: efax

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

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