mkefiboot: 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/mkefiboot - from package: livecd-tools

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

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