mkbootdisk: 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 CentOS possible default full paths are:

/sbin/mkbootdisk - from package: mkbootdisk

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