gjackclock: 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/gjackclock - from package: gjacktransport

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

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