升级到 Ubuntu 20.04 后，我再也无法看到双启动菜单来选择启动 Ubuntu 还是 Windows（8.1）；现在，Ubuntu 会直接启动，先显示我的电脑型号（联想），然后出现一个新屏幕，同时显示我的电脑型号和 Ubuntu。
我曾尝试运行：
sudo update-grub
但那并没有什么作用。
如果这很重要，以下是我的/etc/default/grub
# If you change this file, run 'update-grub' afterwards to update
# /boot/grub/grub.cfg.
# For full documentation of the options in this file, see:
# info -f grub -n 'Simple configuration'
#GRUB_HIDDEN_TIMEOUT=0
#GRUB_HIDDEN_TIMEOUT_QUIET=true
GRUB_TIMEOUT=10
GRUB_DISTRIBUTOR=`lsb_release -i -s 2> /dev/null || echo Debian`
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
GRUB_CMDLINE_LINUX=""
# Uncomment to enable BadRAM filtering, modify to suit your needs
# This works with Linux (no patch required) and with any kernel that obtains
# the memory map information from GRUB (GNU Mach, kernel of FreeBSD ...)
#GRUB_BADRAM="0x01234567,0xfefefefe,0x89abcdef,0xefefefef"
# Uncomment to disable graphical terminal (grub-pc only)
#GRUB_TERMINAL=console
# The resolution used on graphical terminal
# note that you can use only modes which your graphic card supports via VBE
# you can see them in real GRUB with the command `vbeinfo'
#GRUB_GFXMODE=640x480
# Uncomment if you don't want GRUB to pass "root=UUID=xxx" parameter to Linux
#GRUB_DISABLE_LINUX_UUID=true
# Uncomment to disable generation of recovery mode menu entries
#GRUB_DISABLE_RECOVERY="true"
# Uncomment to get a beep at grub start
#GRUB_INIT_TUNE="480 440 1"
编辑：
运行结果sudo efibootmgr
BootCurrent: 000E
Timeout: 0 seconds
BootOrder: 000E,000C,0000,0006,000D,0004,0008,0005,0007,0009,000B
Boot0000* fedora
Boot0001 Setup
Boot0002 Boot Menu
Boot0003 Diagnostic Splash
Boot0004* USB FDD:
Boot0005* ATAPI CD:
Boot0006* USB HDD: Generic Flash Disk
Boot0007* USB CD:
Boot0008* ATA HDD: WDC WD10S21X-24R1BT0-SSHD-8GB
Boot0009* PCI LAN: EFI Network (IPv4)
Boot000A* Lenovo Recovery System
Boot000B* PCI LAN: EFI Network (IPv6)
Boot000C* Fedora
Boot000D* Windows Boot Manager
Boot000E* ubuntu
Boot0019* Lenovo Recovery System