I'm not getting any option to select the OS. The laptop directly boots into Ubuntu (my main OS) even though kali linux is properly installed in about 300 gb. A technical support will be appreciated.
Regards
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Just boot up Ubuntu and run the following command to update your Grub menu:
sudo update-grub
Then, reboot.
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I assume you mean `sudo update-grub`, but don't you also need `sudo grub-install` afterwards? I haven't used grub in a few years, but you used to. – terdon Nov 28 '19 at 17:50
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@terdon [Here is an example](https://askubuntu.com/a/400890/167115) where the other os is Linux Mint. – mchid Nov 28 '19 at 19:05
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Yes, that isn't the question. `update-grub` will detect installed OSs and will write a new `/boot/grub/grub.cfg` file. What I am not completely sure about is whether or not that new file is actually read by grub on boot or if it is copied somewhere by `grub-install`. The old grub (grub1) used to be able to read the file directly and manually editing it would change the menu, but I seem to recall that grub2 does not and you might need the `grub-install` command to make the new config take effect. But, as I said, I'm not sure. – terdon Nov 28 '19 at 19:11
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@terdon Yes, on grub2, changes that I've made to `/boot/grub/grub.cfg` have shown up directly on the grub menu after running `grub-install` including any customization or new OS. However, `update-grub` must be run from the OS that installed the current grub menu or the changes will not take effect. The only time I've had to run `grub-install` is to repair or replace a broken grub using [this method](https://help.ubuntu.com/community/Grub2/Installing#via_ChRoot). – mchid Nov 28 '19 at 19:36
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@terdon However, if you were to make changes to the Kali `/boot/grub/grub.cfg`, you would need to run `update-grub` and `grub-install` on Kali for the changes to take effect because the current grub is linked to Ubuntu. – mchid Nov 28 '19 at 19:40