mmm_agentd: 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_agentd - from package: mysql-mmm-agent

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

On Debian possible default full paths are:

/usr/sbin/mmm_agentd - from package: mysql-mmm-agent

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

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