grub customizer (os-prober) runs forever!

Asked by Tony (aqk) on 2015-10-05

I just replaced my old MSI mainboard with a new ASUS M5A78L board. BUT-
The following problem also happened on the old mainboard.
Running Ubuntu 14.04 LTS (and Windows-10) on desktop with 12 GB RAM, and two 1-TB WD disks.

When I do a Update-grub, it takes about TWO HOURS for it to complete. But it does eventually, and naturally the default OS is Ubuntu.
AND the HD light is on BRIGHT continuously! Does this thing check every disk sector?

So, I try to use Grub-Customizer 6.04 (recently re-installed) to modify the various boot options.
When Grub-Cust starts up, it exhibits the same behaviour- 4 Ubunu kernels quickly found and then OS Prober runs for about 2 hours!
Eventually it finds my Win-10 partition, and then configure my Grub options Default: Win-10, timout: 44, etc)
When I click SAVE, it runs FOREVER! And the HD disk light is on.
  HEY! -
LOL- I am running it now, and as I was typing this, it finally SAVED! Thank goodness!
OK- the SAVE took TWO HOURS! I assume that:
1: It isn't the fault of Grub-Customizer, but the *#@* OS-Prober! Why does OS prober take so long?
2. Why does SAVE take two hours? Does it run OS-PROBER again?

I'd modify Grub manually, as I did in the old days, but Grub-2 is too complicated!
I wish I still had Grub-1. This GRUB-2 must have been designed by a committee!

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Q1: os-prober is a little slow cause it scans all partitions for operating systems. However an average time is 10s, not 2h. The time depends on HDD speed, partition count and used file systems. However there could also be a timeout. You should look for error messages by running "sudo update-grub" on command line.

Q2: Yes, when saving, the whole partition scanning is done again. The idea of grub 2 is a dynamically generated config. This way you'll get new menu entries for operating systems that are installed later. Cause the geration takes some time, it is usually just executed after something was changed and this process generates a static config which will be overwritten when starting generation again. Grub customizer doesn't change this static file itself when saving. Instead it changes the config of the dynamic part. When you'll click save, the dynamic menu config will be written and then grub-mkconfig is used to generate the new static config.

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