GenPage: 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/GenPage - from package: edk2-tools

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

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