mmm_backup: 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/sbin/mmm_backup - from package: mysql-mmm-tools

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

On Debian possible default full paths are:

/usr/sbin/mmm_backup - from package: mysql-mmm-tools

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

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