sff2g3: 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/sff2g3 - from package: mgetty-sendfax

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

On Debian possible default full paths are:

/usr/bin/sff2g3 - from package: mgetty-fax

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

Error in other languages:
sff2g3: bevel nie gevind nie
sff2g3: comandă negăsită
sff2g3: comando não encontrado
sff2g3: commande introuvable
sff2g3: command not found
sff2g3: käsku ei ole
sff2g3: không tìm thấy lệnh
sff2g3: komanda nerasta
sff2g3: Kommando nicht gefunden.
sff2g3: kommandot finns inte
sff2g3: komut yok
sff2g3: nie znaleziono polecenia
sff2g3: níor aimsíodh an t-ordú
sff2g3: no se encontró la orden
sff2g3: no s'ha trobat l'ordre
sff2g3: opdracht niet gevonden
sff2g3: parancs nem található
sff2g3: perintah tidak ditemukan
sff2g3: príkaz nenájdený
sff2g3: příkaz nenalezen
sff2g3: команда не найдена
sff2g3: командата не е открита
sff2g3: 命令找不到
sff2g3: コマンドが見つかりません