mmm_mond: 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_mond - from package: mysql-mmm-monitor

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

On Debian possible default full paths are:

/usr/sbin/mmm_mond - from package: mysql-mmm-monitor

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

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