g3dviewer: 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/g3dviewer - from package: g3dviewer

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

Error in other languages:
g3dviewer: bevel nie gevind nie
g3dviewer: comandă negăsită
g3dviewer: comando não encontrado
g3dviewer: commande introuvable
g3dviewer: command not found
g3dviewer: käsku ei ole
g3dviewer: không tìm thấy lệnh
g3dviewer: komanda nerasta
g3dviewer: Kommando nicht gefunden.
g3dviewer: kommandot finns inte
g3dviewer: komut yok
g3dviewer: nie znaleziono polecenia
g3dviewer: níor aimsíodh an t-ordú
g3dviewer: no se encontró la orden
g3dviewer: no s'ha trobat l'ordre
g3dviewer: opdracht niet gevonden
g3dviewer: parancs nem található
g3dviewer: perintah tidak ditemukan
g3dviewer: príkaz nenájdený
g3dviewer: příkaz nenalezen
g3dviewer: команда не найдена
g3dviewer: командата не е открита
g3dviewer: 命令找不到
g3dviewer: コマンドが見つかりません