修改完 /etc/default/grub ， 需要执行 sudo update-grub 生成 /boot/grub/grub.cfg，重启后生效
update-grub 脚本的实际命令为 grub-mkconfig -o /boot/grub/grub.cfg
注释内容前面有 * 的代表常修改项，有 - 的非特殊用途不修改

# 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=0      // * 默认启动项，按menuentry顺序，从0开始；若改为saved，则默认上次启动项      
#GRUB_HIDDEN_TIMEOUT=0      // - 隐藏菜单，grub2不再使
GRUB_HIDDEN_TIMEOUT_QUIET=true      // - true不显示倒计时，屏幕将会是空白的；false空白屏幕上有计时器
GRUB_TIMEOUT=3      // * 设置进入默认启动项的等候时间，默认值10秒；若为-1则一直等待
GRUB_DISTRIBUTOR=`lsb_release -i -s 2> /dev/null || echo Debian`
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"     // * 添加内核启动参数，这个为默认
GRUB_CMDLINE_LINUX="acpi_osi=Linux"     // * 手动添加内核启动参数，比如 acpi=off noapic等可在这里添加

# 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      // - 设置是否使用图形介面。去除前面#，仅使用控制台终端，不使用图形介面

# 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       // * 设定图形介面分辨率，如不使用默认，把前面#去掉，分辨率按需修改

# Uncomment if you don't want GRUB to pass "root=UUID=xxx" parameter to Linux
#GRUB_DISABLE_LINUX_UUID=true   // - 设置grub命令是否使用UUID，去掉#，使用root=/dev/sdax而不用root=UUDI=xxx

# Uncomment to disable generation of recovery mode menu entries
#GRUB_DISABLE_RECOVERY="true"       // - 设定是否创建修复模式菜单项

# Uncomment to get a beep at grub start
#GRUB_INIT_TUNE="480 440 1"