vtop: 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/sbin/vtop - from package: util-vserver

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

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