fence_ilo3_ssh: 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

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_ilo3_ssh - from package: fence-agents

You may install the required package with command yum install {package}
Error in other languages:
fence_ilo3_ssh: bevel nie gevind nie
fence_ilo3_ssh: comandă negăsită
fence_ilo3_ssh: comando não encontrado
fence_ilo3_ssh: commande introuvable
fence_ilo3_ssh: command not found
fence_ilo3_ssh: käsku ei ole
fence_ilo3_ssh: không tìm thấy lệnh
fence_ilo3_ssh: komanda nerasta
fence_ilo3_ssh: Kommando nicht gefunden.
fence_ilo3_ssh: kommandot finns inte
fence_ilo3_ssh: komut yok
fence_ilo3_ssh: nie znaleziono polecenia
fence_ilo3_ssh: níor aimsíodh an t-ordú
fence_ilo3_ssh: no se encontró la orden
fence_ilo3_ssh: no s'ha trobat l'ordre
fence_ilo3_ssh: opdracht niet gevonden
fence_ilo3_ssh: parancs nem található
fence_ilo3_ssh: perintah tidak ditemukan
fence_ilo3_ssh: príkaz nenájdený
fence_ilo3_ssh: příkaz nenalezen
fence_ilo3_ssh: команда не найдена
fence_ilo3_ssh: командата не е открита
fence_ilo3_ssh: 命令找不到
fence_ilo3_ssh: コマンドが見つかりません