wmmatrix: 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/wmmatrix - from package: wmmatrix

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

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