vpstree: 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/vpstree - from package: util-vserver

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

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