jack_mix_box: 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_mix_box - from package: jack-mixer

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

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