jack_midiseq: 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_midiseq - 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_midiseq - from package: jackd1
/usr/bin/jack_midiseq - from package: jackd2

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

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