vmemctrl: 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/vmemctrl - from package: util-vserver

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

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