我的电脑运行 Ubuntu，无法启动。我已附上日志，boot-repair但不知道该如何修复该问题：
boot-repair-4ppa130 [20210916_0927]
============================== Boot Info Summary ===============================
=> No known boot loader is installed in the MBR of /dev/sda.
=> Syslinux MBR (5.00 and higher) is installed in the MBR of /dev/sdb.
sdb1: __________________________________________________________________________
File system: vfat
Boot sector type: SYSLINUX 6.04
Boot sector info: Syslinux looks at sector 32816 of /dev/sdb1 for its
second stage. The integrity check of Syslinux failed.
No errors found in the Boot Parameter Block.
Operating System:
Boot files: /boot/grub/grub.cfg /syslinux.cfg
/efi/BOOT/grubx64.efi /efi/BOOT/mmx64.efi /ldlinux.sys
================================ 0 OS detected =================================
============================ Architecture/Host Info ============================
CPU architecture: 64-bit
Live-session OS is Ubuntu 64-bit (Ubuntu 20.04.3 LTS, focal, x86_64)
===================================== UEFI =====================================
BIOS is EFI-compatible, and is setup in EFI-mode for this live-session.
No EFI in dmseg.
SecureBoot enabled.
efibootmgr -v
BootCurrent: 0000
Timeout: 0 seconds
BootOrder: 0000,0002
Boot0000* UEFI Lexar USB Flash Drive AACI4MFFHNW7BYBZ PciRoot(0x0)/Pci(0x14,0x0)/USB(1,0)/HD(1,MBR,0x4ee5b1,0x800,0x1dd5800)/File(\EFI\Boot\BootX64.efi)N.....YM....R,Y.
Boot0002* ubuntu HD(1,GPT,1a3d2b6c-f752-48e6-9101-5c8c0fd603ba,0x800,0x177000)/File(\EFI\ubuntu\shimx64.efi)
This session has been detected as 'live' because df -Th / contains overlay
============================= Drive/Partition Info =============================
Disks info: ____________________________________________________________________
Partitions info (1/3): _________________________________________________________
Partitions info (2/3): _________________________________________________________
Partitions info (3/3): _________________________________________________________
fdisk -l (filtered): ___________________________________________________________
Disk sdb: 14.94 GiB, 16018046976 bytes, 31285248 sectors
Disk identifier: 0x004ee5b1
Boot Start End Sectors Size Id Type
sdb1 * 2048 31285247 31283200 14.9G c W95 FAT32 (LBA)
parted -lm (filtered): _________________________________________________________
sda:-512.00B:scsi:512:512:unknown:ATA ST1000LM035-1RK1:;
sdb:16.0GB:scsi:512:512:msdos:Lexar USB Flash Drive:;
1:1049kB:16.0GB:16.0GB:fat32::boot, lba;
blkid (filtered): ______________________________________________________________
NAME FSTYPE UUID PARTUUID LABEL PARTLABEL
sda
sdb
└─sdb1 vfat 2CAF-E43E 004ee5b1-01 UBUNTU 20_0
df (filtered): _________________________________________________________________
Avail Use% Mounted on
sdb1 12G 19% /cdrom
Mount options: __________________________________________________________________
sdb1 ro,noatime,fmask=0022,dmask=0022,codepage=437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro
====================== sdb1/boot/grub/grub.cfg (filtered) ======================
Ubuntu
Ubuntu (safe graphics)
OEM install (for manufacturers)
Boot from next volume
UEFI Firmware Settings
========================= sdb1/syslinux.cfg (filtered) =========================
DEFAULT loadconfig
LABEL loadconfig
CONFIG /isolinux/isolinux.cfg
APPEND /isolinux/
==================== sdb1: Location of files loaded by Grub ====================
GiB - GB File Fragment(s)
?? = ?? boot/grub/grub.cfg 1
================== sdb1: Location of files loaded by Syslinux ==================
GiB - GB File Fragment(s)
?? = ?? syslinux.cfg 1
?? = ?? ldlinux.sys 1
======================== Unknown MBRs/Boot Sectors/etc =========================
Unknown MBR on /dev/sda
=============================== StdErr Messages ================================
ERROR: asr: seeking device "/dev/sda" to 18446744073709550592
ERROR: ddf1: seeking device "/dev/sda" to 18446744073709550592
ERROR: ddf1: seeking device "/dev/sda" to 18446744073709419520
ERROR: hpt37x: seeking device "/dev/sda" to 4608
ERROR: hpt45x: seeking device "/dev/sda" to 18446744073709545472
ERROR: isw: seeking device "/dev/sda" to 18446744073709550080
ERROR: isw: seeking device "/dev/sda" to 18446744073709550592
ERROR: isw: seeking device "/dev/sda" to 18446744073708468224
ERROR: jmicron: seeking device "/dev/sda" to 18446744073709550592
ERROR: lsi: seeking device "/dev/sda" to 18446744073709550592
ERROR: nvidia: seeking device "/dev/sda" to 18446744073709550080
ERROR: pdc: seeking device "/dev/sda" to 137438913024
ERROR: pdc: seeking device "/dev/sda" to 137438920192
ERROR: pdc: seeking device "/dev/sda" to 137438927360
ERROR: pdc: seeking device "/dev/sda" to 137438934528
ERROR: sil: seeking device "/dev/sda" to 18446744073709550592
ERROR: via: seeking device "/dev/sda" to 18446744073709550592
ERROR: asr: seeking device "/dev/sda" to 18446744073709550592
ERROR: ddf1: seeking device "/dev/sda" to 18446744073709550592
ERROR: ddf1: seeking device "/dev/sda" to 18446744073709419520
ERROR: hpt37x: seeking device "/dev/sda" to 4608
ERROR: hpt45x: seeking device "/dev/sda" to 18446744073709545472
ERROR: isw: seeking device "/dev/sda" to 18446744073709550080
ERROR: isw: seeking device "/dev/sda" to 18446744073709550592
ERROR: isw: seeking device "/dev/sda" to 18446744073708468224
ERROR: jmicron: seeking device "/dev/sda" to 18446744073709550592
ERROR: lsi: seeking device "/dev/sda" to 18446744073709550592
ERROR: nvidia: seeking device "/dev/sda" to 18446744073709550080
ERROR: pdc: seeking device "/dev/sda" to 137438913024
ERROR: pdc: seeking device "/dev/sda" to 137438920192
ERROR: pdc: seeking device "/dev/sda" to 137438927360
ERROR: pdc: seeking device "/dev/sda" to 137438934528
ERROR: sil: seeking device "/dev/sda" to 18446744073709550592
ERROR: via: seeking device "/dev/sda" to 18446744073709550592
File descriptor 63 (pipe:[85462]) leaked on lvs invocation. Parent PID 17618: /bin/bash
Suggested repair: ______________________________________________________________
默认修复并未boot-repair解决问题。