hp-systray: 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/hp-systray - from package: hplip-gui

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

On Debian possible default full paths are:

/usr/bin/hp-systray - from package: hplip-gui

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

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