mmg3d4: 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 CentOS possible default full paths are:

/usr/bin/mmg3d4 - from package: mmg3d

You may install the required package with command yum install {package}

Error in other languages:
mmg3d4: bevel nie gevind nie
mmg3d4: comandă negăsită
mmg3d4: comando não encontrado
mmg3d4: commande introuvable
mmg3d4: command not found
mmg3d4: käsku ei ole
mmg3d4: không tìm thấy lệnh
mmg3d4: komanda nerasta
mmg3d4: Kommando nicht gefunden.
mmg3d4: kommandot finns inte
mmg3d4: komut yok
mmg3d4: nie znaleziono polecenia
mmg3d4: níor aimsíodh an t-ordú
mmg3d4: no se encontró la orden
mmg3d4: no s'ha trobat l'ordre
mmg3d4: opdracht niet gevonden
mmg3d4: parancs nem található
mmg3d4: perintah tidak ditemukan
mmg3d4: príkaz nenájdený
mmg3d4: příkaz nenalezen
mmg3d4: команда не найдена
mmg3d4: командата не е открита
mmg3d4: 命令找不到
mmg3d4: コマンドが見つかりません