munin-node: 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/munin-node - from package: munin-node

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

On Debian possible default full paths are:

/usr/sbin/munin-node - from package: munin-node

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

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