rifftree: 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/rifftree - from package: gigtools

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

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