jack-stdin: 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-stdin - from package: jack-stdio

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

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