adt-virt-null: 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/adt-virt-null - from package: autopkgtest

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

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