why does Win sometimes not appear in dual boot grub menu?

[Jake M]

Have been using a Win/ Ubuntu dual boot config for years with either OS
selected at boot up. Occasionally, however, like today, I'll find Win
missing from the menu or the menu won't appear at all at boot up and
goes directly into Ubuntu. This has happened a couple of times over the
last five years. I used boot-repair to fix today (I don't know how I've
fixed in the past), but still wonder why it seems to occur at random
like it does and would welcome your answers. Thanks in advance.

[Jonathan N. Little]

Post by Jake M
Have been using a Win/ Ubuntu dual boot config for years with either OS
selected at boot up.  Occasionally, however, like today, I'll find Win
missing from the menu or the menu won't appear at all at boot up and
goes directly into Ubuntu.  This has happened a couple of times over the
last five years.  I used boot-repair to fix today (I don't know how I've
fixed in the past), but still wonder why it seems to occur at random
like it does and would welcome your answers.  Thanks in advance.

If I had to guess I would say maybe you don't have the os prober enabled
in grub.

Make sure the line in /etc/default/grub exist:

GRUB_DISABLE_OS_PROBER=false

then update grub:

sudo update-grub

and reboot and see if the Windows entry is restored. I cannot remember
when Ubuntu changed the default to disabled the os-prober. I haven't
dual booted in a long time, but it is been awhile I began seeing:

"Warning: os-prober will not be executed to detect other bootable
partitions.
Systems on them will not be added to the GRUB boot configuration.
Check GRUB_DISABLE_OS_PROBER documentation entry."

when updating grub on my systems. This might help explain:

<https://askubuntu.com/questions/1414245/why-do-i-get-warning-os-prober-will-not-be-executed-to-detect-other-bootable-p>

[Paul]

Post by Jonathan N. Little

Post by Jake M
Have been using a Win/ Ubuntu dual boot config for years with either OS
selected at boot up.  Occasionally, however, like today, I'll find Win
missing from the menu or the menu won't appear at all at boot up and
goes directly into Ubuntu.  This has happened a couple of times over the
last five years.  I used boot-repair to fix today (I don't know how I've
fixed in the past), but still wonder why it seems to occur at random
like it does and would welcome your answers.  Thanks in advance.

If I had to guess I would say maybe you don't have the os prober enabled
in grub.
GRUB_DISABLE_OS_PROBER=false
sudo update-grub
and reboot and see if the Windows entry is restored. I cannot remember
when Ubuntu changed the default to disabled the os-prober. I haven't
"Warning: os-prober will not be executed to detect other bootable
partitions.
Systems on them will not be added to the GRUB boot configuration.
Check GRUB_DISABLE_OS_PROBER documentation entry."
<https://askubuntu.com/questions/1414245/why-do-i-get-warning-os-prober-will-not-be-executed-to-detect-other-bootable-p>

You would likely want to check that the os-prober package was installed.
I've had distros before, where that was one of the steps. So that's
two things to check. If os-prober was entirely missing from a repository,
that would be additional work. Sometimes, people forget to enable
"universe" and "multiverse", which contain a lot more packages
than the core ones do.

For example, this is a typical Ubuntu sequence, early on. From my notes file
(so some details may have changed). This is how I arrange my coffee
so it has just the right amount of cream and sugar :-)

sudo add-apt-repository universe
sudo add-apt-repository multiverse
sudo apt-get update
sudo apt-get install synaptic
sudo synaptic

Then you can do the equivalent of this, in the search.

apt search os-prober

os-prober/focal 1.74ubuntu2 amd64
utility to detect other OSes on a set of drives

The changes to boot could be happening on kernel updates.
The kernel update would update the boot menu, as a side effect.
There are also things you can do to /etc/default/grub, to make
a better menu experience (make the ASCII menu appear on the screen for example).

When you do the

sudo update-grub

then the response dumped in the terminal, tells you whether
your dual-boot is being picked up properly. Once you've verified
the entries you expect are there, you can test-boot. There is no
sense testing, until the output indicates a change of mood.

I believe the GRUB version may have also changed, and
that is the most likely candidate for "flicking the light
switches on and off". Normally, if you'd configured things
a certain way, they would "stick". Whereas a GRUB package update
could mess with the controls (like "all good software" must).

Paul

[Bobbie Sellers]

Post by Paul

Post by Jonathan N. Little

Post by Jake M
Have been using a Win/ Ubuntu dual boot config for years with either OS
selected at boot up.  Occasionally, however, like today, I'll find Win
missing from the menu or the menu won't appear at all at boot up and
goes directly into Ubuntu.  This has happened a couple of times over the
last five years.  I used boot-repair to fix today (I don't know how I've
fixed in the past), but still wonder why it seems to occur at random
like it does and would welcome your answers.  Thanks in advance.

If I had to guess I would say maybe you don't have the os prober enabled
in grub.
GRUB_DISABLE_OS_PROBER=false
sudo update-grub
and reboot and see if the Windows entry is restored. I cannot remember
when Ubuntu changed the default to disabled the os-prober. I haven't
"Warning: os-prober will not be executed to detect other bootable
partitions.
Systems on them will not be added to the GRUB boot configuration.
Check GRUB_DISABLE_OS_PROBER documentation entry."
<https://askubuntu.com/questions/1414245/why-do-i-get-warning-os-prober-will-not-be-executed-to-detect-other-bootable-p>

You would likely want to check that the os-prober package was installed.
I've had distros before, where that was one of the steps. So that's
two things to check. If os-prober was entirely missing from a repository,
that would be additional work. Sometimes, people forget to enable
"universe" and "multiverse", which contain a lot more packages
than the core ones do.
For example, this is a typical Ubuntu sequence, early on. From my notes file
(so some details may have changed). This is how I arrange my coffee
so it has just the right amount of cream and sugar :-)
sudo add-apt-repository universe
sudo add-apt-repository multiverse
sudo apt-get update
sudo apt-get install synaptic
sudo synaptic
Then you can do the equivalent of this, in the search.
apt search os-prober
os-prober/focal 1.74ubuntu2 amd64
utility to detect other OSes on a set of drives
The changes to boot could be happening on kernel updates.
The kernel update would update the boot menu, as a side effect.
There are also things you can do to /etc/default/grub, to make
a better menu experience (make the ASCII menu appear on the screen for example).
When you do the
sudo update-grub
then the response dumped in the terminal, tells you whether
your dual-boot is being picked up properly. Once you've verified
the entries you expect are there, you can test-boot. There is no
sense testing, until the output indicates a change of mood.
I believe the GRUB version may have also changed, and
that is the most likely candidate for "flicking the light
switches on and off". Normally, if you'd configured things
a certain way, they would "stick". Whereas a GRUB package update
could mess with the controls (like "all good software" must).
Paul

And a dual-boot Windows-Linux configuration file can be
trashed by Windows kernel updates.

bliss- Dell Precision 7730- PCLOS 2024.02- Linux 6.6.18- Plasma 5.27.10

[Paul]

    And a dual-boot Windows-Linux configuration file can be
trashed by Windows kernel updates.
bliss- Dell Precision 7730- PCLOS 2024.02- Linux 6.6.18- Plasma 5.27.10

Not currently evident.

Upgrades of the OS (23H2), do not change boot materials.
In Linux terms, it is like not using any sort of GRUB software.

The last OS Upgrade was in fact, a Feature Update, which shows
few symptoms of being more than a Patch Tuesday.

it is a Clean Install, which blows away Linux materials. A Clean install,
would be adding a Windows after a Linux (a machine that hasn't seen a Windows, gets one).

+-----+---------+--------------------------+
| MBR | Linux | Install Windows here | Kaboom!
+-----+---------+--------------------------+

Do not install Linux and then install Windows. Instead,
install Windows first, then Linux second, for a dual boot.

This generally behaves OK.

+-----+---------+--------------------------+
| MBR | Windows | Linux | OK
+-----+---------+--------------------------+
22H2 ->
23H2

One of the reasons it is a bit happy, is the EFI partition (FAT32)
has two folders. It has a Ubuntu folder. It has a Windows folder.
Windows materials go into the Windows folder.

When there is no Windows folder in the EFI partition, this will
tempt Windows to write a new first stage boot in the MBR, removing
GRUB first stage boot.

I expect the rules would be a bit different for a legacy boot.
But these days, not many people still do Legacy boot, as there
are device issues doing that. (I don't know if you can do that
on an NVMe drive, or for that matter, on an eMMC. Those might
be UEFI items.) While you can do Extended/Logical on a HDD and
load'er up with OSes, that takes some careful thought to do well.
Maybe some older Windows 10 would have had trouble with that,
doing an Upgrade, but Win10 has stopped doing Upgrades so when you
install, you get 22H2 and that's the end of it. I've only got one
practical Windows 11 install here, so that's not exactly a "popular"
dual boot item here. And its last Upgrade, was a Feature Upgrade,
which is not necessarily the same as a regular Upgrade done with
a DVD. And having a Windows folder in ESP, keeps it happy.

Like everything multi-booters do, "test... and see".

That's how it works. there is too much silly crap in the world now,
to make each and every prediction with a money-back guarantee.

Paul

[Jonathan N. Little]

Post by Paul
You would likely want to check that the os-prober package was installed.
I've had distros before, where that was one of the steps. So that's
two things to check. If os-prober was entirely missing from a repository,
that would be additional work. Sometimes, people forget to enable
"universe" and "multiverse", which contain a lot more packages
than the core ones do.

I think you will find Ubuntu installs it by default. It is just disabled
in the default configuration of grub.

Here on a fresh install of 22.04 *Server* they even install it:

apt-cache policy os-prober
os-prober:
Installed: 1.79ubuntu2
Candidate: 1.79ubuntu2
Version table:
*** 1.79ubuntu2 500
500 http://us.archive.ubuntu.com/ubuntu jammy/main amd64 Packages
100 /var/lib/dpkg/status