运行 Ubuntu 20.04.1 LTS。启动时，我得到一个包含 2 个条目（Ubuntu 和 Advanced）的 grub 菜单，超时时间为 30 秒。我想禁用超时，或者将时间缩短到几秒钟。
这是我的 /etc/default/grub 文件，但超时仍然是 30 秒：
# 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_DEFAULT="saved"
GRUB_TIMEOUT_STYLE="countdown"
GRUB_TIMEOUT="2"
GRUB_DISTRIBUTOR="`lsb_release -i -s 2> /dev/null || echo Debian`"
GRUB_CMDLINE_LINUX_DEFAULT="maybe-ubiquity"
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"
GRUB_RECORDFAIL_TIMEOUT="5"
#GRUB_DISABLE_OS_PROBER="false"
#GRUB_HIDDEN_TIMEOUT="1"
GRUB_SAVEDEFAULT="true"
完整的 /boot/grub/grub.cfg 可以在这里找到https://pastebin.com/qT6rFTvM