gnunet-download-manager: 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/gnunet-download-manager - from package: gnunet

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

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