jackd: 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/jackd - from package: jack-audio-connection-kit

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

On Debian possible default full paths are:

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

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

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