Recover partition table with systemrescue and testdisk

TABLE OF CONTENTS

• Symptom(s)
• Solution
• If it's a boot disk ...

Symptom(s)

Missing partitions in lsblk (or similar) output.

Solution

It is advisable to backup your system before attempting any partition repairs.

In the article below `sdX` is a placeholder, do not literally type sdX.
Make sure to substitute sdX with the correct disk drive.

Boot into systemrescue cd.

To analyse the device and recover lost partitions, run the following, pointing it to the drive with missing partitions. Run the command and follow the prompts:

testdisk /dev/sdX

On a successful discovery of the partition(s) you can 'write' them by 

navigating trough menu options, once done, select 'Quit'.

If it's a boot disk ...

If the disk that lost it's partitions was a boot disk, it will most likely have lost the grub installation too.

To start the recovery of grub, we need to mount the disk.
The process of mounting the partitions will depend on how the machine was set up.
Run `lsblk` again to see all the partitions
The most important partitions is root (/) and when present boot (/boot)

For example:

mount /dev/sdXn /mnt

mount /dev/sdXn /mnt/boot

Rebind the virtual file systems
This is required so that grub has system access to the machine instead of regular jail access:

for i in proc sys dev; do mount -o bind /$i /mnt/$i ; done

chroot /mnt

Fix/Install bootloader 

grub-install /dev/sdX

grub2-install /dev/sdX

exit

grub-install --root-directory=/mnt /dev/sdX