drbl-prepare-memtest: 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/share/drbl/sbin/drbl-prepare-memtest - from package: drbl

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

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