The boot sequence with systemd

[oldhack]

Can any one help with a fix,  for a very slow boot sequence (approx 3 mins) caused by me changing the grub2 boot from a partition to the MBR.
The systemd log shows the boot sequence as trying to find and load a drive that has changed and which it continues to recycle through ( showing the seconds counting down 1min 30) only to fail!
I hope that there is some type of systemd 'purge' action  (- am I dreaming  )

o.

[Dan]

I'll admit that this is beyond my knowledge. However, have you tried running...

sudo update-grub

...in your terminal?

I don't know if that will help, but in my experience, it's always a good idea to update grub when you change something having to do with grub.

[Mike]

Perhaps there is a non-existent partition listed in your fstab?

[oldhack]

Thank you both, Dan and Mike, for your very prompt replies and suggestions and I confirm I have tried both without any success!
I too have almost no knowledge of the boot process, however Grub will not have an impact on this because Grub is only 'pointing' to the root partition to boot and my limited understanding of the issue, is that the subsequent 'system initiation' process (systemd) has a problem finding the original associated partitions. I thought that the UUID drive identifiers took care of any drive ID changes but maybe I understand even less than I thought 

o.

[billwho]

It may be grub and not systemd.

Read about boot-repair:
https://help.ubuntu.com/community/Boot-Repair

Download boot-repair from here:
https://sourceforge.net/p/boot-repair-cd/home/Home/

Create a boot-repair cd or usb drive.
Follow the directions.

Does that fix the problem?

[oldhack]

Thank you billwho for the potential rescue solutions. I will download and check them out.  I have tried a few other solutions  (like rescatux), and you might be correct, Grub could be screwed up. It may take me several days to complete but I will respond with the results.
o.

[oldhack]

I managed to install ( -and download) the 'boot repair' app and ran the code. Regrettably the ISO  - on a USB would not load and run from boot. Presumably the ISO did not have the 'appropriate' coding to run from boot - I don't know, but the install from ubuntu main did run ok.
It seemed to work well and replaced Grub ( -which is what it's main purpose seems to be) and it reported a successful completion. The bad news is that it has not changed the lengthy boot sequence, in fact, systemd reported an increase in time!
In summary, I believe the problem that I reported, systemd not finding (recognizing) a drive UUID, requires a systemd 'purge' (-probably a manual change of UUID line,) which I have not the faintest idea how to do! 
Thank you for your help, but I have now decided to re-install ( I have all my Data backed up).

o.

[billwho]

unetbootin is needed to make a bootable usb of boot-repair iso
these need unetbootin to make a boot usb:
zorin
knoppix
boot-repair
systemrescuecd