Terminal Windows
you have to choose one thing!
Win+R
write: cmd - open administrator
I recommend choosing Linux/GRUB.
bootloader Linux
bcdedit /set {bootmgr} path \EFI\ubuntu\shimx64.efi
bootloader Windows
bcdedit /set {bootmgr} path \EFI\Microsoft\Boot\bootmgfw.efi
full reset bootloader Windows
bcdboot C:\Windows /s C: /f UEFI
Linux Terminal
sudo nano /etc/default/grub
GRUB_DEFAULT=0
GRUB_TIMEOUT_STYLE=menu
GRUB_TIMEOUT=-1
GRUB_DISTRIBUTOR=( . /etc/os-release; echo ${NAME:-Ubuntu} ) 2>/dev/null || echo Ubuntu
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_enforce_resources=lax acpi_enforce_resources=lax"
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_enforce_resources=lax usbcore.autosuspend=-1 split_lock_mitigate=0"
GRUB_CMDLINE_LINUX=""
GRUB_DISABLE_OS_PROBER=false
Ctrl+O, Enter, Ctrl+X
sudo update-grub
++++++++++++++++++++++++++++++++
be careful when enabling security boot - on the Windows bootloader!
if the system writes the keys to the motherboard, only shorting the BIOS battery will help you!
otherwise, a Windows system with security boot enabled - will no longer boot through GRUB.
then the nuance is that when updating the system can kill/delete GRUB itself!
the system can enable recovery by standard, or when updating, pull up other keys for the bootloader - I highly recommend turning it off, completely disabling Windows updates, disabling fast startup and completely deleting the Windows recovery image.
I don't know who needs these broken Windows updates, I completely disabled them, I'm sitting with security booting via GRUB - I deleted the default recovery image, regarding updates, the standard antivirus can update databases during system startup (in the scheduler).
Auto_Update_Defender-SYSTEM-AtStartup-SignatureUpdate -MMPC
C:\Program Files\Windows Defender\MpCmdRun.exe
PS C:\WINDOWS\system32> Register-ScheduledTask -TaskName "Auto_Update_Defender" -Action (New-ScheduledTaskAction -Execute "C:\Program Files\Windows Defender\MpCmdRun.exe" -Argument "-SignatureUpdate -MMPC") -Trigger (New-ScheduledTaskTrigger -AtStartup) -Settings (New-ScheduledTaskSettingsSet -AllowStartIfOnBatteries -DontStopIfGoingOnBatteries) -User "NT AUTHORITY\SYSTEM" -RunLevel Highest -Force
MpCmdRun: Command Line: "C:\Program Files\Windows Defender\MpCmdRun.exe" -SignatureUpdate -MMPC
Start Time: Пн чер 15 2026 20:19:08
MpEnsureProcessMitigationPolicy(0x5): hr = 0x1
Start: MpSignatureUpdate()
Service Version: 4.18.26050.15
Engine Version: 1.1.26050.11
AntiSpyware Signature Version: 1.453.108.0
AntiVirus Signature Version: 1.453.108.0
Calling MpUpdateStartEx with option 0x11
Update started
Search Started (Direct HTTP) (Path: https://go.microsoft.com/fwlink/?LinkID=851034&clcid=0x409&arch=x64&eng=1.1.26050.11&avdelta=1.453.108.0&asdelta=1.453.108.0&prod=77BDAF73-B396-481F-9042-AD358843EC24&ostype=0&signaturetype=0&beta=0&plat=4.18.26050.15&OsVersion=10.0.26100.8457&altlocation=0)...
Installation Completed
Search Started (Direct HTTP) (Path: https://go.microsoft.com/fwlink/?LinkID=870379&clcid=0x409&arch=x64&eng=1.1.26050.11&avdelta=1.453.108.0&asdelta=1.453.108.0&prod=77BDAF73-B396-481F-9042-AD358843EC24&ostype=0&signaturetype=0&beta=0&plat=4.18.26050.15&OsVersion=10.0.26100.8457&altlocation=0)...
Installation Completed
Update completed succesfully . no updates needed (hr:0x00000001)
Finish: MpSignatureUpdate()
MpCmdRun: End Time: Пн чер 15 2026 20:19:09
for those who want to have fun, there is an exit Security Boot - Enable> BIOS-Custom> add bootloader keys to manual mode "Enroll Efi Image"
execution method - Query User
