dtnperf_vION: 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/dtnperf_vION - from package: ion

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

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