gt5: 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/gt5 - from package: gt5

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

Error in other languages:
gt5: bevel nie gevind nie
gt5: comandă negăsită
gt5: comando não encontrado
gt5: commande introuvable
gt5: command not found
gt5: käsku ei ole
gt5: không tìm thấy lệnh
gt5: komanda nerasta
gt5: Kommando nicht gefunden.
gt5: kommandot finns inte
gt5: komut yok
gt5: nie znaleziono polecenia
gt5: níor aimsíodh an t-ordú
gt5: no se encontró la orden
gt5: no s'ha trobat l'ordre
gt5: opdracht niet gevonden
gt5: parancs nem található
gt5: perintah tidak ditemukan
gt5: príkaz nenájdený
gt5: příkaz nenalezen
gt5: команда не найдена
gt5: командата не е открита
gt5: 命令找不到
gt5: コマンドが見つかりません