wmu: 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/wmu - from package: wml

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

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