marble-qt: 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/marble-qt - from package: marble-qt

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

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