virt-builder: 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/virt-builder - from package: libguestfs-tools

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

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