My ‘system disk’ (/dev/sda) started to show bad sectors, recently, and so I decided to replace it.    The disk was around 8 years old, and had been in almost-continuous use..

I have not had to do this for some considerable time, and I think the last time was in the late-90s, and using LILO!  (No convoluted grub2 commands and UUIDs back then..)

I found – after some trials – that one successful way of doing this is mentioned in an article here, and thanks to Arif for the information:    https://ask.fedoraproject.org/en/question/31666/how-do-you-install-grub2-on-a-replacement-hard-drive/

I created a (Fedora 23) netinst image on a USB stick, and booted from this, and ran the ‘rescue’ utility…    The system only had a USB2 connection, so the utility was very sluggish, but I found that I could get a command prompt by typing alt/tab.. I mounted the ‘new’ root partition (/dev/sda2) under /mnt/sysimage (/run/media/liveuser/newdiskroot in the example), and mounted the (separate) boot partition (/dev/sda1) under /mnt/sysimage/boot..    I had decided to use btrfs for the ‘new’ root partition, but – being over-cautious – kept the boot partition as ext4..

After running the (modified) commands mentioned in the article – and remembering to update /etc/fstab – the system booted correctly..

This is – of course – rather Fedora-specific, but it is possible to get dracut on other Distros..

Robert Gadsdon.   June 2, 2016.