xpenguins-stop: 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/xpenguins-stop - from package: xpenguins

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

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