stumpwm: 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/stumpwm - from package: stumpwm

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

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