dfu-prefix: 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/dfu-prefix - from package: dfu-util

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

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