jack-plumbing: 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-plumbing - from package: jack-tools

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

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