fence_ipdu: 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/fence_ipdu - from package: fence-agents

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

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