jack-udp: 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/jack-udp - from package: jack-tools

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

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