Well, yes, but the problem is that /etc/fstab resides on whatever the default root subvolume is set to, and the default root subvolume is the one with subvolid=5, while Calamares configures the actual root directory (and thus /etc/fstab) to reside on a subvolume named @, which has a different subvolid.
For manjaro-chroot, they might indeed create obstacles. The read-only aspect of /usr is less important in that regard.
Fiddlling about in the filesystem - what I do know is not a production system - just a playground
$ ls /mnt
@ @cache @home @log
Yes, thatās what Calamares installs the system root directory into, but to btrfs itself, it is not the default root of the filesystem.
You can set/change the default ā i.e. the subvolume that gets mounted if no specific subvol= or subvolid= mount option is provided ā by way of the btrfs command, similar to how one would use tune2fs for setting certain options on an ext2/ext3/ext4 filesystem. This default will then be stored in the filesystem itself.
Addendum: Upon checking my own system here, Iāve come across thisā¦ 
[nx-74205:/dev/pts/3][/home/aragorn]
[aragorn] > ls -l /var/lock/
total 8
-rw-r--r-- 1 root root 22 Jun 20 01:29 asound.state.lock
-rw-r--r-- 1 root root 22 Jun 20 01:29 card0.lock
drwxrwxrwt 2 root root 40 Jun 20 01:29 dmraid
drwxr-xr-x 2 root root 40 Jun 20 01:29 subsys
drwx------ 2 root root 40 Jun 23 21:33 timeshift
[nx-74205:/dev/pts/3][/home/aragorn]
[aragorn] > ls -l /var/lock/dmraid/
total 0
So the directory /var/lock/dmraid/ should normally exist already, and it should have the sticky bit set. 
So what do you guys suggest I try now?
Is there other mounts I have to mount?
The only one failing is sudo mount -t efivarfs efivarfs /sys/firmware/efi/efivars, it says itās already mounted otherwise if I do the following I can chroot into my system, but the error ERROR: mkdir /var/lock/dmraid is still present while update-grub.
sudo mount -o subvol=@ /dev/sda7 /mnt
sudo mount --bind /dev /mnt/dev
sudo mount -t proc proc /mnt/proc
sudo mount -t sysfs sys /mnt/sys
#sudo mount -t efivarfs efivarfs /sys/firmware/efi/efivars (says it's already mounted so I do not run this)
sudo mount -t vfat /dev/sda5 /mnt/boot/efi
sudo chroot /mnt /bin/bash
Advice still needed. Iām crossing my fingers @linux-aarhus is running his test rig at a speed that it produces 
and will come back with the most intricate analysis in existence. xD
See the addendum to my previous post. 
It looks like you are doing the grub-boot-iso dance.
If you - instead of using the 40_custom file - use the /boot/grub/custom.cfg - it wonāt break your grub - and if you make a mistake - it still doesnāt break your grub.
I just checked my system and yes, like yours but for some reason there is a lvm and card1.lock that you donāt have.
Should I check what it looks like in live?
IIRC it was empty, but my memory is not the same it was a few years ago so I will check that and come back,
From my system, non-live:
ls -l /var/lock/
total 12
-rw-r--r-- 1 root root 22 Jun 24 14:10 asound.state.lock
-rw-r--r-- 1 root root 22 Jun 24 14:10 card0.lock
-rw-r--r-- 1 root root 22 Jun 24 14:10 card1.lock
drwxrwxrwt 2 root root 40 Jun 24 12:13 dmraid
drwx------ 2 root root 40 Jun 24 12:13 lvm
drwxr-xr-x 2 root root 40 Jun 24 12:13 subsys
drwxr-xr-x 2 root root 40 Jun 24 15:00 timeshift
ls -l /var/lock/dmraid
total 0
On another note, how do you guys make the preformated text into those āfoldableā buttons here on the forum?
Aaah, I will try that, I just used the 40_custom file because its easier to keep things in order. Do you think the 40_custom file is unreadable with update-grub and that is why it throws the error?
I will try that as well and see if that changes anything and come back and report.
I can update my grub config on a btrfs system using the following steps - assuming a default Calamares install - your system appears from the previous fstab to a default Calamares install
sudo mount /dev/sda2 /mnt
sudo mount /dev/sda1 /mnt/@/boot/efi
sudo mount --bind /mnt/@cache /mnt/@/var/cache
sudo mount --bind /mnt/@home /mnt/@/home
sudo mount --bind /mnt/@log /mnt/@/var/log
sudo manjaro-chroot /mnt/@ /bin/bash
Do your config changes - what you need to do.
If you need to update grub you can safely ignore the message ERROR: mkdir /var/lock/dmraid - the configuration will be updated as you expect.
When you are done - exit the chroot
exit
And reboot the system
If you use the -o subvol=@ mount option for mounting the on-disk root filesystem to /mnt, then you donāt need to specify the @/ in the paths for the subsequent target mounpoints. Also, you donāt have to use bind-mounts if you mount the subvolumes directly via the subvol option.
sudo mount -t btrfs -o subvol=@ /dev/sda2 /mnt
sudo mount -t vfat /dev/sda1 /mnt/boot/efi
sudo mount -t btrfs -o subvol=@cache /dev/sda2 /mnt/var/cache
sudo mount -t btrfs -o subvol=@home /dev/sda2 /mnt/home
sudo mount -t btrfs -o subvol=@log /dev/sda2 /mnt/var/log
sudo manjaro-chroot /mnt/ /bin/bash
I managed to hook the 2 most awesome āmanjaro dudesā here on the forum, you are both FANTASTIC! 
I have a few things to test out now and will get to it, probably later this evening and then come back with reports.
THANK YOU FROM THE BOTTOM OF MY HEART!!! 
Edit
@linux-aarhus my offer to that game still stands btw, I havenāt forgotten, just throw me a dm if you want to. No preassure ofc! <3
Update:
JUST when starting to type this update, 3 lines in to be exact, I realized one crucial thing I COMPLETELY forgot about, and I can not expect you to pick that up through the tiny hints that are there.
As you can see I have my / at sda7, the reason, I also have a windows 11 installation, the os-prober never mentions finding windows, so that is probably where it fails?
Itās still strange though, the grub menu should not be completely disabled, the snapshots are found.
Example of a WORKING update-grub:
Generating grub configuration file ...
Found theme: /usr/share/grub/themes/manjaro/theme.txt
Found linux image: /boot/vmlinuz-6.1-x86_64
Found initrd image: /boot/amd-ucode.img /boot/initramfs-6.1-x86_64.img
Found initrd fallback image: /boot/initramfs-6.1-x86_64-fallback.img
Found linux image: /boot/vmlinuz-5.15-x86_64
Found initrd image: /boot/amd-ucode.img /boot/initramfs-5.15-x86_64.img
Found initrd fallback image: /boot/initramfs-5.15-x86_64-fallback.img
Warning: os-prober will be executed to detect other bootable partitions.
Its output will be used to detect bootable binaries on them and create new boot entries.
Found Windows Boot Manager on /dev/sda1@/efi/Microsoft/Boot/bootmgfw.efi
Adding boot menu entry for UEFI Firmware Settings ...
Detecting snapshots ...
Found snapshot: 2023-06-23 18:00:01 | timeshift-btrfs/snapshots/2023-06-23_18-00-01/@ | daily | N/A |
Found snapshot: 2023-06-22 18:00:01 | timeshift-btrfs/snapshots/2023-06-22_18-00-01/@ | daily | N/A |
Found snapshot: 2023-06-21 18:00:01 | timeshift-btrfs/snapshots/2023-06-21_18-00-01/@ | daily | N/A |
Found snapshot: 2023-06-20 20:22:27 | timeshift-btrfs/snapshots/2023-06-20_20-22-27/@ | ondemand | {timeshift-autosnap} {created before upgrade} |
Found snapshot: 2023-06-20 18:00:01 | timeshift-btrfs/snapshots/2023-06-20_18-00-01/@ | daily | N/A |
Found snapshot: 2023-06-20 17:00:01 | timeshift-btrfs/snapshots/2023-06-20_17-00-01/@ | weekly | N/A |
Found snapshot: 2023-06-19 18:00:01 | timeshift-btrfs/snapshots/2023-06-19_18-00-01/@ | daily | N/A |
Found snapshot: 2023-06-18 18:00:02 | timeshift-btrfs/snapshots/2023-06-18_18-00-02/@ | daily | N/A |
Found snapshot: 2023-06-17 18:00:01 | timeshift-btrfs/snapshots/2023-06-17_18-00-01/@ | daily | N/A |
Found snapshot: 2023-06-16 21:47:16 | timeshift-btrfs/snapshots/2023-06-16_21-47-16/@ | ondemand | {timeshift-autosnap} {created before upgrade} |
Found snapshot: 2023-06-15 21:29:16 | timeshift-btrfs/snapshots/2023-06-15_21-29-16/@ | ondemand | {timeshift-autosnap} {created before upgrade} |
Found snapshot: 2023-06-13 17:00:01 | timeshift-btrfs/snapshots/2023-06-13_17-00-01/@ | weekly | N/A |
Found snapshot: 2023-06-06 21:33:25 | timeshift-btrfs/snapshots/2023-06-06_21-33-25/@ | ondemand | N/A |
Found snapshot: 2023-06-06 17:00:01 | timeshift-btrfs/snapshots/2023-06-06_17-00-01/@ | weekly | N/A |
Found snapshot: 2023-06-05 23:00:08 | timeshift-btrfs/snapshots/2023-06-05_23-00-08/@ | monthly | N/A |
Found snapshot: 2023-05-30 17:00:01 | timeshift-btrfs/snapshots/2023-05-30_17-00-01/@ | weekly | N/A |
Found snapshot: 2023-05-30 14:28:02 | timeshift-btrfs/snapshots/2023-05-30_14-28-02/@ | ondemand | N/A |
Found snapshot: 2023-05-29 01:58:22 | timeshift-btrfs/snapshots/2023-05-29_01-58-22/@ | ondemand | N/A |
Found snapshot: 2023-05-29 00:48:57 | timeshift-btrfs/snapshots/2023-05-29_00-48-57/@ | ondemand | N/A |
Found snapshot: 2023-05-25 20:54:40 | timeshift-btrfs/snapshots/2023-05-25_20-54-40/@ | ondemand | N/A |
Found snapshot: 2023-05-05 23:00:02 | timeshift-btrfs/snapshots/2023-05-05_23-00-02/@ | monthly | N/A |
Found 21 snapshot(s)
Unmount /tmp/grub-btrfs.uOi9myYczu .. Success
Found memtest86+ image: /boot/memtest86+/memtest.bin
Found memtest86+ EFI image: /boot/memtest86+/memtest.efi
done
Note: Found Windows Boot Manager on /dev/sda1@/efi/Microsoft/Boot/bootmgfw.efi
Maybe itās ONLY the os prober at play here, and everything else works?
I wonāt go through the whole process I went through, the conclusion is the error is consistent no matter how I mount, the manjaro-chroot works if I do the process you guys gave me, I can also su bedna and all seems to work.
cache log and home is probably not needed if I stay as root.
sudo mount -t btrfs -o subvol=@ /dev/sda7 /mnt &&
sudo mount -t vfat /dev/sda5 /mnt/boot/efi &&
sudo mount -t btrfs -o subvol=@cache /dev/sda7 /mnt/var/cache &&
sudo mount -t btrfs /dev/sda8 /mnt/home &&
sudo mount -t btrfs -o subvol=@log /dev/sda7 /mnt/var/log &&
sudo manjaro-chroot /mnt /bin/bash
Again, I removed every extra menu item created by removing the 40_custom file so only the windows 11 is the āout of the ordinaryā now.
Edit
There is a file called 41_custom though that I do NOT recognize, should that be there??
#!/bin/sh
cat <<EOF
if [ -f \${config_directory}/custom.cfg ]; then
source \${config_directory}/custom.cfg
elif [ -z "\${config_directory}" -a -f \$prefix/custom.cfg ]; then
source \$prefix/custom.cfg
fi
EOF
ls /etc/grub.d
00_header 10_linux 20_linux_xen 30_os-prober 30_uefi-firmware 35_fwupd 41_custom 41_snapshots-btrfs 60_memtest86+ 60_memtest86+-efi README
Edit 2
Do you want me to start a new thread? Or change the name of it or something?
That path is wrong. /dev/sda1 is a device special file, not a directory. Therefore, it cannot have any subdirectory named @ or efi below it, and it cannot be a mountpoint.
Furthermore, the device as spelled out above is /dev/sda1@, which I donāt even think exists ā btrfs subvolumes are not block devices, only the parent partition is.
Disclaimer: I donāt use Microsoft Windows and I have only one operating system on my computer. Therefore I am also not using os-prober, and I have no idea how it works. 
I have no idea, all I can say is it works, the windows option is in my grub menu and It works to boot. I used it yesterday to shrink a ntfs volume to fit the iso files that started all this. xD
Iām going to try to boot into windows right after this to see that it still works, but pretty sure that line has looked like that forever for me.
So where do I go from here? Is this a grub issue or who manages the os_prober scripts. Is there anywhere I can request support?
Even though I feeeeel like this is a manjaro thing (im running manjaro, using manjaro-chroot), it might not also be the correct place to ask for help?
Edit
Yepp, hello, this is a robot typing from windows 11ā¦ xD
Iām sorry, but now Iām sriously getting confused as to what the problem isā¦
ā¦ and in the same postā¦
Yes, it exists on my system as well.
Sorry. I was probably unclear.
The line Found Windows Boot Manager on /dev/sda1@/efi/Microsoft/Boot/bootmgfw.efi does not exist when running update-grub within a chroot session. The log containing that line is from my REAL system running update-grub
chroot session: (fails after os-prober and grub menu is gone, booting straight into manjaro)
Generating grub configuration file ...
Found theme: /usr/share/grub/themes/manjaro/theme.txt
Found linux image: /boot/vmlinuz-6.1-x86_64
Found initrd image: /boot/amd-ucode.img /boot/initramfs-6.1-x86_64.img
Found initrd fallback image: /boot/initramfs-6.1-x86_64-fallback.img
Found linux image: /boot/vmlinuz-5.15-x86_64
Found initrd image: /boot/amd-ucode.img /boot/initramfs-5.15-x86_64.img
Found initrd fallback image: /boot/initramfs-5.15-x86_64-fallback.img
Warning: os-prober will be executed to detect other bootable partitions.
Its output will be used to detect bootable binaries on them and create new boot entries.
ERROR: mkdir /var/lock/dmraid
Adding boot menu entry for UEFI Firmware Settings ...
Detecting snapshots ...
Found snapshot: 2023-06-23 18:00:01 | timeshift-btrfs/snapshots/2023-06-23_18-00-01/@ | daily | N/A |
Found snapshot: 2023-06-22 18:00:01 | timeshift-btrfs/snapshots/2023-06-22_18-00-01/@ | daily | N/A |
Found snapshot: 2023-06-21 18:00:01 | timeshift-btrfs/snapshots/2023-06-21_18-00-01/@ | daily | N/A |
Found snapshot: 2023-06-20 20:22:27 | timeshift-btrfs/snapshots/2023-06-20_20-22-27/@ | ondemand | {timeshift-autosnap} {created before upgrade} |
Found snapshot: 2023-06-20 18:00:01 | timeshift-btrfs/snapshots/2023-06-20_18-00-01/@ | daily | N/A |
Found snapshot: 2023-06-20 17:00:01 | timeshift-btrfs/snapshots/2023-06-20_17-00-01/@ | weekly | N/A |
Found snapshot: 2023-06-19 18:00:01 | timeshift-btrfs/snapshots/2023-06-19_18-00-01/@ | daily | N/A |
Found snapshot: 2023-06-18 18:00:02 | timeshift-btrfs/snapshots/2023-06-18_18-00-02/@ | daily | N/A |
Found snapshot: 2023-06-17 18:00:01 | timeshift-btrfs/snapshots/2023-06-17_18-00-01/@ | daily | N/A |
Found snapshot: 2023-06-16 21:47:16 | timeshift-btrfs/snapshots/2023-06-16_21-47-16/@ | ondemand | {timeshift-autosnap} {created before upgrade} |
Found snapshot: 2023-06-15 21:29:16 | timeshift-btrfs/snapshots/2023-06-15_21-29-16/@ | ondemand | {timeshift-autosnap} {created before upgrade} |
Found snapshot: 2023-06-13 17:00:01 | timeshift-btrfs/snapshots/2023-06-13_17-00-01/@ | weekly | N/A |
Found snapshot: 2023-06-06 21:33:25 | timeshift-btrfs/snapshots/2023-06-06_21-33-25/@ | ondemand | N/A |
Found snapshot: 2023-06-06 17:00:01 | timeshift-btrfs/snapshots/2023-06-06_17-00-01/@ | weekly | N/A |
Found snapshot: 2023-06-05 23:00:08 | timeshift-btrfs/snapshots/2023-06-05_23-00-08/@ | monthly | N/A |
Found snapshot: 2023-05-30 17:00:01 | timeshift-btrfs/snapshots/2023-05-30_17-00-01/@ | weekly | N/A |
Found snapshot: 2023-05-30 14:28:02 | timeshift-btrfs/snapshots/2023-05-30_14-28-02/@ | ondemand | N/A |
Found snapshot: 2023-05-29 01:58:22 | timeshift-btrfs/snapshots/2023-05-29_01-58-22/@ | ondemand | N/A |
Found snapshot: 2023-05-29 00:48:57 | timeshift-btrfs/snapshots/2023-05-29_00-48-57/@ | ondemand | N/A |
Found snapshot: 2023-05-25 20:54:40 | timeshift-btrfs/snapshots/2023-05-25_20-54-40/@ | ondemand | N/A |
Found snapshot: 2023-05-05 23:00:02 | timeshift-btrfs/snapshots/2023-05-05_23-00-02/@ | monthly | N/A |
Found 21 snapshot(s)
Unmount /tmp/grub-btrfs.PpCgm3PZbz .. Success
Found memtest86+ image: /boot/memtest86+/memtest.bin
Found memtest86+ EFI image: /boot/memtest86+/memtest.efi
done
MY system, right now: (everything works perfectly, win11 entry is in grub boot menu)
Generating grub configuration file ...
Found theme: /usr/share/grub/themes/manjaro/theme.txt
Found linux image: /boot/vmlinuz-6.1-x86_64
Found initrd image: /boot/amd-ucode.img /boot/initramfs-6.1-x86_64.img
Found initrd fallback image: /boot/initramfs-6.1-x86_64-fallback.img
Found linux image: /boot/vmlinuz-5.15-x86_64
Found initrd image: /boot/amd-ucode.img /boot/initramfs-5.15-x86_64.img
Found initrd fallback image: /boot/initramfs-5.15-x86_64-fallback.img
Warning: os-prober will be executed to detect other bootable partitions.
Its output will be used to detect bootable binaries on them and create new boot entries.
Found Windows Boot Manager on /dev/sda1@/efi/Microsoft/Boot/bootmgfw.efi
Adding boot menu entry for UEFI Firmware Settings ...
Detecting snapshots ...
Found snapshot: 2023-06-24 19:04:21 | timeshift-btrfs/snapshots/2023-06-24_19-04-21/@ | daily | N/A |
Found snapshot: 2023-06-23 18:00:01 | timeshift-btrfs/snapshots/2023-06-23_18-00-01/@ | daily | N/A |
Found snapshot: 2023-06-22 18:00:01 | timeshift-btrfs/snapshots/2023-06-22_18-00-01/@ | daily | N/A |
Found snapshot: 2023-06-21 18:00:01 | timeshift-btrfs/snapshots/2023-06-21_18-00-01/@ | daily | N/A |
Found snapshot: 2023-06-20 20:22:27 | timeshift-btrfs/snapshots/2023-06-20_20-22-27/@ | ondemand | {timeshift-autosnap} {created before upgrade} |
Found snapshot: 2023-06-20 18:00:01 | timeshift-btrfs/snapshots/2023-06-20_18-00-01/@ | daily | N/A |
Found snapshot: 2023-06-20 17:00:01 | timeshift-btrfs/snapshots/2023-06-20_17-00-01/@ | weekly | N/A |
Found snapshot: 2023-06-19 18:00:01 | timeshift-btrfs/snapshots/2023-06-19_18-00-01/@ | daily | N/A |
Found snapshot: 2023-06-18 18:00:02 | timeshift-btrfs/snapshots/2023-06-18_18-00-02/@ | daily | N/A |
Found snapshot: 2023-06-16 21:47:16 | timeshift-btrfs/snapshots/2023-06-16_21-47-16/@ | ondemand | {timeshift-autosnap} {created before upgrade} |
Found snapshot: 2023-06-15 21:29:16 | timeshift-btrfs/snapshots/2023-06-15_21-29-16/@ | ondemand | {timeshift-autosnap} {created before upgrade} |
Found snapshot: 2023-06-13 17:00:01 | timeshift-btrfs/snapshots/2023-06-13_17-00-01/@ | weekly | N/A |
Found snapshot: 2023-06-06 21:33:25 | timeshift-btrfs/snapshots/2023-06-06_21-33-25/@ | ondemand | N/A |
Found snapshot: 2023-06-06 17:00:01 | timeshift-btrfs/snapshots/2023-06-06_17-00-01/@ | weekly | N/A |
Found snapshot: 2023-06-05 23:00:08 | timeshift-btrfs/snapshots/2023-06-05_23-00-08/@ | monthly | N/A |
Found snapshot: 2023-05-30 17:00:01 | timeshift-btrfs/snapshots/2023-05-30_17-00-01/@ | weekly | N/A |
Found snapshot: 2023-05-30 14:28:02 | timeshift-btrfs/snapshots/2023-05-30_14-28-02/@ | ondemand | N/A |
Found snapshot: 2023-05-29 01:58:22 | timeshift-btrfs/snapshots/2023-05-29_01-58-22/@ | ondemand | N/A |
Found snapshot: 2023-05-29 00:48:57 | timeshift-btrfs/snapshots/2023-05-29_00-48-57/@ | ondemand | N/A |
Found snapshot: 2023-05-25 20:54:40 | timeshift-btrfs/snapshots/2023-05-25_20-54-40/@ | ondemand | N/A |
Found snapshot: 2023-05-05 23:00:02 | timeshift-btrfs/snapshots/2023-05-05_23-00-02/@ | monthly | N/A |
Found 21 snapshot(s)
Unmount /tmp/grub-btrfs.Re9LGDAUTs .. Success
Found memtest86+ image: /boot/memtest86+/memtest.bin
Found memtest86+ EFI image: /boot/memtest86+/memtest.efi
done
This, to me, suggests that your live session and your installed version are not both booting in native UEFI mode. I even suspect that itās the live session that boots in legacy BIOS emulation mode, because as far as I know ā but then again, itās Microsoft Windows, and I donāt use that OS ā Windows 11 requires a native UEFI boot.
What this means concretely is that if you have two operating systems on the same drive that boot in different modes ā i.e. one in native UEFI mode and the other in legacy BIOS mode ā then os-prober will not detect the one running in the other mode. Considering that it does detect your Windows installation when running from the installed Manjaro, the Manjaro installation must be the one booting in native UEFI mode, but for some reason, your live installation did not.
Try disabling legacy BIOS emulation (CSM) in the UEFI settings utility and see whether it makes a difference.
Set GRUB_TIMEOUT_STYLE=menu in /etc/default/grub and then run sudo update-grub.
Ok, donāt be mad at me nowā¦ takes deep breath
I have had GRUB_TIMEOUT_STYLE=hidden in my grub config sinceā¦ well I started using Manjaro. I recall reading up on the setting and pushing it away as āhiding the timeout doesnāt work, I still see itā and just left it at that.
For some reason, maybe you can explain why, when I run sudo update grub normally, the grub menu shows after boot, but if I do it in a live sesh, suddenly the menu dissapears.
So if I change the setting to GRUB_TIMEOUT_STYLE=menu I can run update-grub in live, but the win11 is still not detected.
With GRUB_TIMEOUT_STYLE=hidden the menu still āwaits for my inputā, I know this because I changed my timeout to 20, and my bootscreen (press del to enter bios) kept showing, for 20s. And if I retried, then pressing enter during that time, yeah, it started loading.
So 2 steps forward, 1 step back. xD
CSM was disabled
The usb def boots into UEFI (the second one is a ventoy, I tried using it and booting both ānormalā and in āgrub2 modeā whatever that means, but no difference)
