tiff2fax: 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:

/var/spool/hylafax/bin/tiff2fax - from package: hylafax+-client

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

On Debian possible default full paths are:

/var/spool/hylafax/bin/tiff2fax - from package: hylafax-server

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

Error in other languages:
tiff2fax: bevel nie gevind nie
tiff2fax: comandă negăsită
tiff2fax: comando não encontrado
tiff2fax: commande introuvable
tiff2fax: command not found
tiff2fax: käsku ei ole
tiff2fax: không tìm thấy lệnh
tiff2fax: komanda nerasta
tiff2fax: Kommando nicht gefunden.
tiff2fax: kommandot finns inte
tiff2fax: komut yok
tiff2fax: nie znaleziono polecenia
tiff2fax: níor aimsíodh an t-ordú
tiff2fax: no se encontró la orden
tiff2fax: no s'ha trobat l'ordre
tiff2fax: opdracht niet gevonden
tiff2fax: parancs nem található
tiff2fax: perintah tidak ditemukan
tiff2fax: príkaz nenájdený
tiff2fax: příkaz nenalezen
tiff2fax: команда не найдена
tiff2fax: командата не е открита
tiff2fax: 命令找不到
tiff2fax: コマンドが見つかりません