HackMD
Note: How to fix issue "system bootloader not found error"
Overview:
因應需求，製作完畢一可攜式OS-USB（ubuntu）後，出現UEFI無法順利導引至boot loader，進而導致開機失敗（進入UEFI Shell），如下圖：
- The image was uploaded to a note which you don't have access to
- The note which the image was originally uploaded to has been deleted
Root cause analysis
開機流程（以LINUX為例）：
根據上圖，如在載入EFI system partition（ESP）失敗，則會進入UEFI shell或是退回BIOS，甚至進入無限迴圈，與當前狀況大致符合，於是產生兩個假設：
- 無法正確辨認ESP
- 無法正確辨認bootloader所導致
第一個假設的請況下，解決方案相當簡單：
重新製作一個USB系統碟，並在安裝階段多切割一塊partition，供存放initrd和kernel文件；也就是將/boot路徑下的config獨立存放，issue is fixed！！
如圖：
- Image Not Showing Possible Reasons
- The image was uploaded to a note which you don't have access to
- The note which the image was originally uploaded to has been deleted
- Image Not Showing Possible Reasons
- The image was uploaded to a note which you don't have access to
- The note which the image was originally uploaded to has been deleted
- Image Not Showing Possible Reasons
- The image was uploaded to a note which you don't have access to
- The note which the image was originally uploaded to has been deleted
然而這樣出現兩個問題：
- 以往製作的、釋出的系統碟工具，都可能面臨重工的問題
- 這次的系統碟工具，客戶方有可能需要在"不啟動"情況下存入/修改內部設置文件，而安裝當初，第三個partition增加了lvm2，不僅增加掛載的複雜度，更有掛載失敗的可能性
於是嘗試從第二個假設著手：分析/修改bootloader
最初構思的解法也是如此，並參照了以下方法：
Fix bootloadder
然而失敗，經過分析的結果，確定bootloader有以下檔案：
- BOOTX64.CSV
- grub.cfg
- mmx64.efi
- shimix64.efi
- grubx64.efi
其中，grub.cfg載明關於grub的各類參數，與此案較無關係
Image Not Showing Possible Reasons- The image was uploaded to a note which you don't have access to
- The note which the image was originally uploaded to has been deleted
workflow如下：
其中，修改BOOTX64.CSV的部份是將路徑預設值修改成/EFI/BOOT/BOOTX64.efi
在分析檔案結構時，發現是：自動生成的BOOTX64.efi無法被正確識別；然而在UEFI shell底下可以順利執行grubx64.efi並進入OS，所以解決方案如下：
將自動產生之BOOTX64.EFI刪除後，將grubx64.efi複製到/EFI/BOOT/，並命名為BOOTX64.EFI
附圖是可順利開機和無法順利開機之兩組系統碟目錄結構比較：
- 可順利開機：Image Not Showing Possible Reasons
- The image was uploaded to a note which you don't have access to
- The note which the image was originally uploaded to has been deleted
- 無法順利開機：Image Not Showing Possible Reasons
- The image was uploaded to a note which you don't have access to
- The note which the image was originally uploaded to has been deleted
（經實驗證明，與檔案大小寫無關連，所以單純修改檔名並無效用；BOOT.bak是筆者建立的備份資料夾，並非自然產生）
Commands
commands
修改指令如下，可先建立備份資料夾（BOOT.bak）以防誤刪檔案：
command: cp /boot/efi/EFI/BOOT* /boot/efi/EFI/BOOT.bak
command: rm /boot/efi/EFI/BOOT/*
command: cp /boot/efi/EFI/BOOT.bak/fbx64.efi /boot/efi/EFI/BOOT/
command: cp /boot/efi/EFI/BOOT.bak/mmx64.efi /boot/efi/EFI/BOOT/
command: cp /boot/efi/EFI/ubuntu/fbx64.efi /boot/efi/EFI/BOOT/BOOTX64.efi
執行擷圖：
- The image was uploaded to a note which you don't have access to
- The note which the image was originally uploaded to has been deleted
之後斷電，重新使用調整完畢的系統碟開機即可
Ref.
Fix bootloader
initrd & initramfs
GRUB 2
開機流程
The correlation between EFI、boot loading config & linux distribution
bootOrder not found
