總有人裝了Ubuntu仍忘不了Windows。我在剛接觸linux 的時候也是這樣，不過現在好了很多，如果不是必須要用Windows 的時候，我一般都選擇進入Ubuntu。為了那些剛使用Ubuntu的人方便進入Windows，也為了以後有人再問我的時候，我可以很輕松明了的回答ta。特意在此記下GRUB2是如何修改默認引導系統的。
在網上Google或Baidu一下，結果會出來很多，我大致看了一下，絕大部分內容雷同，基本都是讓你修改/boot/grub/grub.cfg。沒錯，無論過程怎麼樣結果都是grub.cfg被修改。但是在這個文件的開頭它已經清清楚楚的告訴你：DO NOT EDIT THIS FILE。grub.cfg不應該手動被修改。
為了方便起見，我把如何修改默認引導系統Copy過來，如下：
grub (/etc/default/grub)
This file contains information previously found in the upper section of /boot/grub/menu.lst. It contains settings primarily affecting Grub's menu display. This file can be edited by root to make changes to these settings; they will be imported into grub.cfg when "update-grub" is executed.
# If you change this file, run 'update-grub' afterwards to update
# /boot/grub/grub.cfg.
GRUB_DEFAULT=0
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 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 entrys
#GRUB_DISABLE_LINUX_RECOVERY="true"
This file contains information formerly contained in the upper section of Grub Legacy's ''menu.lst'' and items contained on the end of the kernel line. The items in this file can be edited by a user with administrator (root) privileges. Grub developers have have placed explanatory comments within the file itself.
GRUB_DEFAULT=0
Sets the default and pre-selected menu entry. Entries may be numeric or saved
GRUB_DEFAULT=0
Sets the default menu entry by menu position. As with Grub Legacy, the first "menuentry" in grub.cfg is 0, the second is 1, etc.
GRUB_DEFAULT="Windows XP Professional (on /dev/sda1)"
Sets the default menu entry by name.
GRUB_DEFAULT=saved
Sets the default menu entry with either whatever was selected on the last boot (if SAVEDEFAULT=true is set and the entry itself contains savedefault), whatever the last grub-set-default command saved or the first entry if nothing has ever been saved or the saved entry can't be found. If the menu is displayed during boot, the previously selected option will be highlighted. If no action is taken, this is selection which will be booted at the end of the timeout, or if the menu is hidden.
GRUB_TIMEOUT=10
No change from Grub Legacy. This is the number of seconds before the default entry is automatically booted.
Setting a value of -1 will display the menu until the user makes a selection (no timeout).
GRUB_HIDDEN_TIMEOUT=0
The hidden timeout option is available to single-OS computers - if multiple OS's are known to Grub 2, this option is bypassed.
On single-OS systems, the menu will be hidden unless a # symbol is present at the beginning of this line. ( # GRUB_HIDDEN_TIMEOUT=0 )
The default setting initially depends on the presence of other operating systems.
Another OS Detected: The menu will be displayed. ( The line will begin with a # symbol. )
No other OS Detected: This setting is not used, as determined by the
For integers greater than 0, the system will pause, but not display the menu, for the entered number of seconds.
0 The menu will not be displayed. There will be no delay.
The user may force displaying the menu as the computer boots by holding down the SHIFT key (single-OS computers only).
During boot, the system will check the SHIFT key status. If it cannot determine the key status, a short delay will enable the user to display the menu by pressing the ESC key.
If enabled, the splash screen designated in 05_debian_theme will be displayed even if the hidden menu feature is selected.
GRUB_HIDDEN_TIMEOUT_QUIET=true
true - No countdown is displayed. The screen will be blank.
false - A counter will display on a blank screen for the duration of the GRUB_HIDDEN_TIMEOUT value.
GRUB_DISTRIBUTOR=lsb_release -i -s 2> /dev/null || echo Debian
Determines the descriptive name in the menu entry. (Ubuntu, Xubuntu, Debian, etc.)
GRUB_CMDLINE_LINUX
If it exists, this line imports any entries to the end of the linux command line (Grub Legacy's "kernel" line) for both normal and recovery modes. This is similar to the "altoptions" line in menu.lst
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
This line imports any entries to the end of the 'linux' line (Grub Legacy's "kernel" line). The entries are appended to the end of the normal mode only. This is similar to the "defoptions" line in menu.lst. If you want a black screen with scrolling boot messages, remove "quiet splash". If you want a grub splash screen with limited messages underneath the Ubuntu logo, use only "splash". < This [only "splash"]will not work in Karmic during boot as the xsplash does not display the messages , but the messages at shutdown will be displayed.
#GRUB_TERMINAL=console
Uncomment to disable graphical terminal (grub-pc only).
#GRUB_GFXMODE=640x480
Uncomment (remove '#' from beginning of the line) to change (increase) resolution of your boot loader. Use one of classic (4:3 rate):
GRUB_GFXMODE=640x480 (is used if isn't here a proper value)
GRUB_GFXMODE=800x600
GRUB_GFXMODE=1024x768
GRUB_GFXMODE=1600×1200
or make experiments with some others nonstandards like widescreen (16:10 ratio in my case), here is list of most of commonly use Display resolution:
GRUB_GFXMODE=640x400
GRUB_GFXMODE=800x500
GRUB_GFXMODE=1024x640
GRUB_GFXMODE=1280x800
GRUB_GFXMODE=1680x1050
If you don't know what modes are supported by your graphics card, go to the grub command line and run 'vbeinfo'. It will list all available modes. (You might need to run 'insmod vbe' first if the vbe module isn't loaded yet)
GRUB_GFXPAYLOAD_LINUX=640x480x8 [grub2 >= 1.98-1 (Lucid)]
Use this setting to set the framebuffer resolution (replaces the vga= kernel option). It uses the GFXMODE values with additional color depth. Use 'vbeinfo' from the grub command line to list what modes are available to you.
#GRUB_DISABLE_LINUX_UUID=true
Uncomment this line if you don't want GRUB to pass "root=UUID=xxx" parameter to Linux.
GRUB_DISABLE_LINUX_RECOVERY=true
Add or uncomment this line to prevent "Recovery" mode kernel options from appearing in the menu.
GRUB_DISABLE_OS_PROBER=true
Enables/disables the os-prober check of other partitions for operating systems, including Windows, Linux, OSX and Hurd.
