munin-run: 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-run - 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-run - from package: munin-node

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

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