gxtuner: 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/gxtuner - from package: gxtuner

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

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