How to rescue your partition tables with gpart - and reinstall grub in Red Hat

Extending disk in vmware.
All the partition tables are missing. Whole disc are unallocated.

start with gpart livecd
Start with gpart /dev/sda (searching for missing partition tables in sda) Write down your cylinder.
Start parted
-unit s
-rescue
--start (cylinder number 'start' in partition1)
--end (cylinder number 'end' in partition1)

Repeat that if you have more than one partition.

You will now find sda1 and sda2 in /dev/*.

Sda1 = boot (ok)
sda2 = / (ok)
sda3 = SWAP-sda3 (I recreate a new swap disk with gpart, it is not necessary but it is far easier because sda3 has many links around the configuration files in my system.)

mount sda2 to /mnt/sda2/
mount sda1 to /mnt/sda2/boot/

go too /mnt/sda2/sbin/
start: grub-installation /dev/sda2
installing grub.

It perfectly works.

In some cases you also need to reconfigure the network card.
nano /etc/sysconfig/network-scripts/ifcg-eth0 .