munin-node-c: command not found

Have You tried accessing the binary with the full path?

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 Debian possible default full paths are:

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

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