Reboot, and choose from the menu the OS you want.

I tried doing that grub command with os-prober installed. Wierd thing is after I tried it. I didn't see anything new pop up after restarting the computer.

If it doesn't work (update-grub should add every OS into boot menu) you can try to setup dual boot manually: https://unix.stackexchange.com/question … -grub-menu

I got a small laptop i am experimenting with for a dual boot setup. I am trying to figure out how to setup dual boot option with devuan and primeOS installed at the same time. I am searching on how to instructions to do this online.

What is the simplest way to setup dual boot option?

I'll be setting up a couple of dual-boot microSD cards today, if these unopened packages on my desk contain a WIFI card that actually works with both linux and Windows-10, and the storage cards i ordered.  It'll probably take a couple hours, but once you get it set up, it's a matter of using it.

I cheat.  Maybe that's my themesong lol.  Here is how i do it:

1. write a new ms-dos partition table to empty media.

2. quiesce all the OS's on your source system that you want to include.  for example, i run Devuan-ascii and Debian-jessie along with Ubuntu-oneiric.  Jessie is my go-to for this kind of operation... not that i can't use Devuan-ascii for it, but Devuan is my go-to OS for normal use, so it's easier if i run jessie to copy the quiesced Devuan partition, then reboot and use Devuan to copy jessie and oneiric onto the target media.

3.  run gparted or equivalent, to see how much space you need on the target media.  create the partitions at this point.  generally what i do is allocate 15gb for Devuan since it's still in daily use and may need more space.  If memory serves, i allocate 10g for jessie and 6g for oneric.  It's a matter of your usage.  I keep all of my user-data in a separate partition, and use a bind-mount in fstab to hook things up.

4.  make sure that you create at least 2 *primary* partitions, or create one and leave space for another.  there are some systems, forex the Dell xps-13, which are "windows-intended" so to speak, and their BIOS plays hardball with the Windows rue about booting only from a primary partition.  Once i have a primary partition of Devuan-ascii, and space left for ceres or whatever when it goes stable, i make the
remainder of the media into an extended partition.  In the extended partition are any other OS's (in my case oneiric) and partitions for my data.

5.  once you have your partitions laid out (this all takes about 10 minutes so far), pick a primary OS.  copy the quiesced OS to the new media (i use rsync because file-by-file is faster than dd etc, and probably always will be unless your partition is maybe 90% full.

6. after you've copied all your installed-and-running (but quiesced) OS, or multiple OS's and data partitions, you're 75% of the say there.

7.  the next step is to edit the copied /etc/fstab files.  use the UUID option to identify partitions, not dev-name or label; UUID is most unique and least problem-prone.

8.  in addition to fstab, you also need a swap partition to act as a suspend/resume device.  You need to put its UUID in the fstab for that OS so it doesn't hang up forever on boot while it times out waiting for the suspend/resume device which it won't find because you never assigned/updated it.  (bug, in startup, imo).  offhand i forget the filename that has to be updated (there are at least 2 different ones based on OS) something like blah/blah/resume.conf  Then you need to update initramfs so the booting OS can find the suspend/resume info.

9.  at this point it's a matter of hooking up grub.  imo grub sucks.  i wrote utilities years ago to do all this crap.  Whatever; it can be done manually, but it's nice to be able to get all your device information placed in the clipboard by poking one key, etc.

Of course if you want to fiddle with grub and its os-probes, the previous replies might probably do the job; i gave up on using the regular grub procedures years ago, because imo they are garbage.

Hey, i'm old and prejudiced, and i've done this "set up a multi-boot" thing more than a few times over the past 10 years or so.  Good luck, you'll figure it out with some help from your friends.

What is the simplest way to setup dual boot option?