GnuGenBootSector: 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/GnuGenBootSector - from package: edk2-tools

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

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