munin-check: 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/bin/munin-check - from package: munin

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

On Debian possible default full paths are:

/usr/bin/munin-check - from package: munin

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

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