jack_session_notify: 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 CentOS possible default full paths are:

/usr/bin/jack_session_notify - from package: jack-audio-connection-kit-example-clients

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/jack_session_notify - from package: jackd1
/usr/bin/jack_session_notify - from package: jackd2

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

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