dtn2fw: 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/dtn2fw - from package: ion

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

Error in other languages:
dtn2fw: bevel nie gevind nie
dtn2fw: comandă negăsită
dtn2fw: comando não encontrado
dtn2fw: commande introuvable
dtn2fw: command not found
dtn2fw: käsku ei ole
dtn2fw: không tìm thấy lệnh
dtn2fw: komanda nerasta
dtn2fw: Kommando nicht gefunden.
dtn2fw: kommandot finns inte
dtn2fw: komut yok
dtn2fw: nie znaleziono polecenia
dtn2fw: níor aimsíodh an t-ordú
dtn2fw: no se encontró la orden
dtn2fw: no s'ha trobat l'ordre
dtn2fw: opdracht niet gevonden
dtn2fw: parancs nem található
dtn2fw: perintah tidak ditemukan
dtn2fw: príkaz nenájdený
dtn2fw: příkaz nenalezen
dtn2fw: команда не найдена
dtn2fw: командата не е открита
dtn2fw: 命令找不到
dtn2fw: コマンドが見つかりません