Update con redhat-upgrade tool de rhel 6.x a 7.x

cat /etc/redhat-release
yum update
subscription-manager repos --enable rhel-6-server-extras-rpms
yum update

yum -y install preupgrade-assistant preupgrade-assistant-el6toel7 preupgrade-assistant-tools
preupg -v

yum -y install redhat-upgrade-tool
yum -y install yum-utils

yum-config-manager --disable *

DESDE LA CONSOLA SI O SI!!!!!!

[root@app1 ~]

# redhat-upgrade-tool --network 7.6 --instrepo http://10.76.40.120/7.6/7Server/x86_64/

Configurar la red especialmente los archivos de route-ethXX

reiniciar y cuando todo funcione reinstalar grub

yum remove grub
yum install grub2
grub2-install --grub-setup=/bin/true /dev/sda
grub2-mkconfig -o /boot/grub2/grub.cfg
vi /boot/grub/grub.conf
agregar
title GRUB 2 Test
root (hd0,0)
kernel /grub2/i386-pc/core.img
boot

reboot #####y seleccionar la opcion grub2 test


si funca ya esta casi listo solo corremos lo siguiente

grub2-install /dev/sda