ledmon: 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/ledmon - from package: ledmon

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

On Debian possible default full paths are:

/usr/sbin/ledmon - from package: ledmon

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

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