GenBootSector: 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/GenBootSector - from package: edk2-tools

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

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