w9wm: 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/w9wm - from package: w9wm

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

Error in other languages:
w9wm: bevel nie gevind nie
w9wm: comandă negăsită
w9wm: comando não encontrado
w9wm: commande introuvable
w9wm: command not found
w9wm: käsku ei ole
w9wm: không tìm thấy lệnh
w9wm: komanda nerasta
w9wm: Kommando nicht gefunden.
w9wm: kommandot finns inte
w9wm: komut yok
w9wm: nie znaleziono polecenia
w9wm: níor aimsíodh an t-ordú
w9wm: no se encontró la orden
w9wm: no s'ha trobat l'ordre
w9wm: opdracht niet gevonden
w9wm: parancs nem található
w9wm: perintah tidak ditemukan
w9wm: príkaz nenájdený
w9wm: příkaz nenalezen
w9wm: команда не найдена
w9wm: командата не е открита
w9wm: 命令找不到
w9wm: コマンドが見つかりません