硬盘的分区表格式是GUID的，所有的引导都会放置在一个fat32的ESP隐藏分区里面，我原先的系统是windows8.1，在这个环境下面，分出来50个G来安装ubuntu16.04操作系统，按照步骤安装完成之后，不会出现只能进入windows8.1这个系统，什么都不做的话都能进入系统选择界面，安装ubuntu16.04之后，默认的引导是ubuntu的grub程序，最主要的一个配置文件是/boot/grub/grub.cfg配置，下面我将我电脑上的这个配置贴出来：
#
# DO NOT EDIT THIS FILE
#
# It is automatically generated by grub-mkconfig using templates
# from /etc/grub.d and settings from /etc/default/grub
#
### BEGIN /etc/grub.d/00_header ###
if [ -s $prefix/grubenv ]; then
set have_grubenv=true
load_env
fi
if [ "${next_entry}" ] ; then
set default="${next_entry}"
set next_entry=
save_env next_entry
set boot_once=true
else
set default="0"
fi
if [ x"${feature_menuentry_id}" = xy ]; then
menuentry_id_option="--id"
else
menuentry_id_option=""
fi
export menuentry_id_option
if [ "${prev_saved_entry}" ]; then
set saved_entry="${prev_saved_entry}"
save_env saved_entry
set prev_saved_entry=
save_env prev_saved_entry
set boot_once=true
fi
function savedefault {
if [ -z "${boot_once}" ]; then
saved_entry="${chosen}"
save_env saved_entry
fi
}
function recordfail {
set recordfail=1
if [ -n "${have_grubenv}" ]; then if [ -z "${boot_once}" ]; then save_env recordfail; fi; fi
}
function load_video {
if [ x$feature_all_video_module = xy ]; then
insmod all_video
else
insmod efi_gop
insmod efi_uga
insmod ieee1275_fb
insmod vbe
insmod vga
insmod video_bochs
insmod video_cirrus
fi
}
if [ x$feature_default_font_path = xy ] ; then
font=unicode
else
insmod part_gpt
insmod ext2
set root='hd0,gpt8'
if [ x$feature_platform_search_hint = xy ]; then
search --no-floppy --fs-uuid --set=root --hint-bios=hd0,gpt8 --hint-efi=hd0,gpt8 --hint-baremetal=ahci0,gpt8 4ea9abbf-1ff0-442c-b5a4-7ee6db251e0a
else
search --no-floppy --fs-uuid --set=root 4ea9abbf-1ff0-442c-b5a4-7ee6db251e0a
fi
font="/share/grub/unicode.pf2"
fi
if loadfont $font ; then
set gfxmode=auto
load_video
insmod gfxterm
set locale_dir=$prefix/locale
set lang=zh_CN
insmod gettext
fi
terminal_output gfxterm
if [ "${recordfail}" = 1 ] ; then
set timeout=30
else
if [ x$feature_timeout_style = xy ] ; then
set timeout_style=menu
set timeout=10
# Fallback normal timeout code in case the timeout_style feature is
# unavailable.
else
set timeout=10
fi
fi
### END /etc/grub.d/00_header ###
### BEGIN /etc/grub.d/05_debian_theme ###
set menu_color_normal=white/black
set menu_color_highlight=black/light-gray
if background_color 44,0,30,0; then
clear
fi
### END /etc/grub.d/05_debian_theme ###
### BEGIN /etc/grub.d/10_linux ###
function gfxmode {
set gfxpayload="${1}"
if [ "${1}" = "keep" ]; then
set vt_handoff=vt.handoff=7
else
set vt_handoff=
fi
}
if [ "${recordfail}" != 1 ]; then
if [ -e ${prefix}/gfxblacklist.txt ]; then
if hwmatch ${prefix}/gfxblacklist.txt 3; then
if [ ${match} = 0 ]; then
set linux_gfx_mode=keep
else
set linux_gfx_mode=text
fi
else
set linux_gfx_mode=text
fi
else
set linux_gfx_mode=keep
fi
else
set linux_gfx_mode=text
fi
export linux_gfx_mode
menuentry 'Ubuntu' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-simple-5aa4c845-d1c3-4466-9f3b-19188a11e88c' {
recordfail
load_video
gfxmode $linux_gfx_mode
insmod gzio
if [ x$grub_platform = xxen ]; then insmod xzio; insmod lzopio; fi
insmod part_gpt
insmod ext2
set root='hd0,gpt7'
if [ x$feature_platform_search_hint = xy ]; then
search --no-floppy --fs-uuid --set=root --hint-bios=hd0,gpt7 --hint-efi=hd0,gpt7 --hint-baremetal=ahci0,gpt7 8309c187-d72e-4085-aa54-a6064f5841db
else
search --no-floppy --fs-uuid --set=root 8309c187-d72e-4085-aa54-a6064f5841db
fi
linux /vmlinuz-4.4.0-22-generic.efi.signed root=UUID=5aa4c845-d1c3-4466-9f3b-19188a11e88c ro quiet splash $vt_handoff
initrd /initrd.img-4.4.0-22-generic
}
#submenu 'Ubuntu 高级选项' $menuentry_id_option 'gnulinux-advanced-5aa4c845-#d1c3-4466-9f3b-19188a11e88c' {
# menuentry 'Ubuntu，Linux 4.4.0-22-generic' --class ubuntu --class gnu-linux --class gnu --#class os $menuentry_id_option 'gnulinux-4.4.0-22-generic-advanced-5aa4c845-#d1c3-4466-9f3b-19188a11e88c' {
# recordfail
# load_video
# gfxmode $linux_gfx_mode
# insmod gzio
# if [ x$grub_platform = xxen ]; then insmod xzio; insmod lzopio; fi
# insmod part_gpt
# insmod ext2
# set root='hd0,gpt7'
# if [ x$feature_platform_search_hint = xy ]; then
# search --no-floppy --fs-uuid --set=root --hint-bios=hd0,gpt7 --hint-efi=hd0,gpt7 #--hint-baremetal=ahci0,gpt7 8309c187-d72e-4085-aa54-a6064f5841db
# else
# search --no-floppy --fs-uuid --set=root 8309c187-d72e-4085-aa54-a6064f5841db
# fi
# echo '载入 Linux 4.4.0-22-generic ...'
# linux /vmlinuz-4.4.0-22-generic.efi.signed root=UUID=5aa4c845-#d1c3-4466-9f3b-19188a11e88c ro quiet splash $vt_handoff
# echo '载入初始化内存盘...'
# initrd /initrd.img-4.4.0-22-generic
# }
# menuentry 'Ubuntu, with Linux 4.4.0-22-generic (upstart)' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-4.4.0-22-generic-init-upstart-5aa4c845-d1c3-4466-9f3b-19188a11e88c' {
# recordfail
# load_video
# gfxmode $linux_gfx_mode
# insmod gzio
# if [ x$grub_platform = xxen ]; then insmod xzio; insmod lzopio; fi
# insmod part_gpt
# insmod ext2
# set root='hd0,gpt7'
# if [ x$feature_platform_search_hint = xy ]; then
# search --no-floppy --fs-uuid --set=root --hint-bios=hd0,gpt7 --hint-efi=hd0,gpt7 --hint-baremetal=ahci0,gpt7 8309c187-d72e-4085-aa54-a6064f5841db
# else
# search --no-floppy --fs-uuid --set=root 8309c187-d72e-4085-aa54-a6064f5841db
# fi
# echo '载入 Linux 4.4.0-22-generic ...'
# linux /vmlinuz-4.4.0-22-generic.efi.signed root=UUID=5aa4c845-d1c3-4466-9f3b-19188a11e88c ro quiet splash $vt_handoff init=/sbin/upstart
# echo '载入初始化内存盘...'
# initrd /initrd.img-4.4.0-22-generic
# }
# menuentry 'Ubuntu, with Linux 4.4.0-22-generic (recovery mode)' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-4.4.0-22-generic-recovery-5aa4c845-d1c3-4466-9f3b-19188a11e88c' {
# recordfail
# load_video
# insmod gzio
# if [ x$grub_platform = xxen ]; then insmod xzio; insmod lzopio; fi
# insmod part_gpt
# insmod ext2
# set root='hd0,gpt7'
# if [ x$feature_platform_search_hint = xy ]; then
# search --no-floppy --fs-uuid --set=root --hint-bios=hd0,gpt7 --hint-efi=hd0,gpt7 --hint-baremetal=ahci0,gpt7 8309c187-d72e-4085-aa54-a6064f5841db
# else
# search --no-floppy --fs-uuid --set=root 8309c187-d72e-4085-aa54-a6064f5841db
# fi
# echo '载入 Linux 4.4.0-22-generic ...'
# linux /vmlinuz-4.4.0-22-generic.efi.signed root=UUID=5aa4c845-d1c3-4466-9f3b-19188a11e88c ro recovery nomodeset
# echo '载入初始化内存盘...'
# initrd /initrd.img-4.4.0-22-generic
# }
# menuentry 'Ubuntu，Linux 4.4.0-21-generic' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-4.4.0-21-generic-advanced-5aa4c845-d1c3-4466-9f3b-19188a11e88c' {
# recordfail
# load_video
# gfxmode $linux_gfx_mode
# insmod gzio
# if [ x$grub_platform = xxen ]; then insmod xzio; insmod lzopio; fi
# insmod part_gpt
# insmod ext2
# set root='hd0,gpt7'
# if [ x$feature_platform_search_hint = xy ]; then
# search --no-floppy --fs-uuid --set=root --hint-bios=hd0,gpt7 --hint-efi=hd0,gpt7 --hint-baremetal=ahci0,gpt7 8309c187-d72e-4085-aa54-a6064f5841db
# else
# search --no-floppy --fs-uuid --set=root 8309c187-d72e-4085-aa54-a6064f5841db
# fi
# echo '载入 Linux 4.4.0-21-generic ...'
# linux /vmlinuz-4.4.0-21-generic.efi.signed root=UUID=5aa4c845-d1c3-4466-9f3b-19188a11e88c ro quiet splash $vt_handoff
# echo '载入初始化内存盘...'
# initrd /initrd.img-4.4.0-21-generic
# }
# menuentry 'Ubuntu, with Linux 4.4.0-21-generic (upstart)' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-4.4.0-21-generic-init-upstart-5aa4c845-d1c3-4466-9f3b-19188a11e88c' {
# recordfail
# load_video
# gfxmode $linux_gfx_mode
# insmod gzio
# if [ x$grub_platform = xxen ]; then insmod xzio; insmod lzopio; fi
# insmod part_gpt
# insmod ext2
# set root='hd0,gpt7'
# if [ x$feature_platform_search_hint = xy ]; then
# search --no-floppy --fs-uuid --set=root --hint-bios=hd0,gpt7 --hint-efi=hd0,gpt7 --hint-baremetal=ahci0,gpt7 8309c187-d72e-4085-aa54-a6064f5841db
# else
# search --no-floppy --fs-uuid --set=root 8309c187-d72e-4085-aa54-a6064f5841db
# fi
# echo '载入 Linux 4.4.0-21-generic ...'
# linux /vmlinuz-4.4.0-21-generic.efi.signed root=UUID=5aa4c845-d1c3-4466-9f3b-19188a11e88c ro quiet splash $vt_handoff init=/sbin/upstart
# echo '载入初始化内存盘...'
# initrd /initrd.img-4.4.0-21-generic
# }
# menuentry 'Ubuntu, with Linux 4.4.0-21-generic (recovery mode)' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-4.4.0-21-generic-recovery-5aa4c845-d1c3-4466-9f3b-19188a11e88c' {
# recordfail
# load_video
# insmod gzio
# if [ x$grub_platform = xxen ]; then insmod xzio; insmod lzopio; fi
# insmod part_gpt
# insmod ext2
# set root='hd0,gpt7'
# if [ x$feature_platform_search_hint = xy ]; then
# search --no-floppy --fs-uuid --set=root --hint-bios=hd0,gpt7 --hint-efi=hd0,gpt7 --hint-baremetal=ahci0,gpt7 8309c187-d72e-4085-aa54-a6064f5841db
# else
# search --no-floppy --fs-uuid --set=root 8309c187-d72e-4085-aa54-a6064f5841db
# fi
# echo '载入 Linux 4.4.0-21-generic ...'
# linux /vmlinuz-4.4.0-21-generic.efi.signed root=UUID=5aa4c845-d1c3-4466-9f3b-19188a11e88c ro recovery nomodeset
# echo '载入初始化内存盘...'
# initrd /initrd.img-4.4.0-21-generic
# }
#}
### END /etc/grub.d/10_linux ###
### BEGIN /etc/grub.d/20_linux_xen ###
### END /etc/grub.d/20_linux_xen ###
### BEGIN /etc/grub.d/20_memtest86+ ###
### END /etc/grub.d/20_memtest86+ ###
### BEGIN /etc/grub.d/30_os-prober ###
menuentry 'Windows 8.1' --class windows --class os $menuentry_id_option 'osprober-efi-000F-0352' {
insmod part_gpt
insmod fat
set root='hd0,gpt1'
if [ x$feature_platform_search_hint = xy ]; then
search --no-floppy --fs-uuid --set=root --hint-bios=hd0,gpt1 --hint-efi=hd0,gpt1 --hint-baremetal=ahci0,gpt1 000F-0352
else
search --no-floppy --fs-uuid --set=root 000F-0352
fi
chainloader /EFI/Microsoft/Boot/bootmgfw.efi
}
set timeout_style=menu
if [ "${timeout}" = 0 ]; then
set timeout=10
fi
### END /etc/grub.d/30_os-prober ###
### BEGIN /etc/grub.d/30_uefi-firmware ###
#menuentry 'System setup' $menuentry_id_option 'uefi-firmware' {
# fwsetup
#}
### END /etc/grub.d/30_uefi-firmware ###
### BEGIN /etc/grub.d/40_custom ###
# This file provides an easy way to add custom menu entries. Simply type the
# menu entries you want to add after this comment. Be careful not to change
# the 'exec tail' line above.
### END /etc/grub.d/40_custom ###
### BEGIN /etc/grub.d/41_custom ###
if [ -f ${config_directory}/custom.cfg ]; then
source ${config_directory}/custom.cfg
elif [ -z "${config_directory}" -a -f $prefix/custom.cfg ]; then
source $prefix/custom.cfg;
fi
### END /etc/grub.d/41_custom ###这个配置的写法感觉就是shell脚本，这个文件是ubuntu自动生成的，一般情况可以不用改。
里面以#开头的是批注，可以不用看，我们需要看的就是前面以menuentry开头的内容，这个内容所代表的就是开机页面启动显示的系统引导，例如：
menuentry 'Windows 8.1' --class windows --class os $menuentry_id_option 'osprober-efi-000F-0352' {
insmod part_gpt
insmod fat
set root='hd0,gpt1'
if [ x$feature_platform_search_hint = xy ]; then
search --no-floppy --fs-uuid --set=root --hint-bios=hd0,gpt1 --hint-efi=hd0,gpt1 --hint-baremetal=ahci0,gpt1 000F-0352
else
search --no-floppy --fs-uuid --set=root 000F-0352
fi
chainloader /EFI/Microsoft/Boot/bootmgfw.efi
}在grub.cfg里面，我上面的内容代表的我windows8.1的引导，如果没有这个内容，那么将无法进入windows8.1。
chainloader /EFI/Microsoft/Boot/bootmgfw.efi，这个代表我电脑里面windows8.1系统的启动管理所存在的位置，同理我电脑上面的ubuntu系统的引导配置：
menuentry 'Ubuntu' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-simple-5aa4c845-d1c3-4466-9f3b-19188a11e88c' {
recordfail
load_video
gfxmode $linux_gfx_mode
insmod gzio
if [ x$grub_platform = xxen ]; then insmod xzio; insmod lzopio; fi
insmod part_gpt
insmod ext2
set root='hd0,gpt7'
if [ x$feature_platform_search_hint = xy ]; then
search --no-floppy --fs-uuid --set=root --hint-bios=hd0,gpt7 --hint-efi=hd0,gpt7 --hint-baremetal=ahci0,gpt7 8309c187-d72e-4085-aa54-a6064f5841db
else
search --no-floppy --fs-uuid --set=root 8309c187-d72e-4085-aa54-a6064f5841db
fi
linux /vmlinuz-4.4.0-22-generic.efi.signed root=UUID=5aa4c845-d1c3-4466-9f3b-19188a11e88c ro quiet splash $vt_handoff
initrd /initrd.img-4.4.0-22-generic
}这个就是我系统里面的ubuntu引导。
在这个配置下面还有许多加了注释的引导，例如ubuntu高级选项和Sytem setup这两个引导，这是我自己加上了注释，ubuntu生成这个grub.cfg的时候是没有注释的，那个时候开机启动的时候显示4个选项，第一个进入ubuntu，第三个进入windows8.1，剩余的两个基本没什么用，所以我为了界面简化，加上了的注释。
这里面还有一些其他配置，里面开机时候出现系统选择引导界面默认等待时间，可以修改:
if [ x$feature_timeout_style = xy ] ; then
set timeout_style=menu
set timeout=10
# Fallback normal timeout code in case the timeout_style feature is
# unavailable.
else
set timeout=10
fi
set timeout_style=menu
if [ "${timeout}" = 0 ]; then
set timeout=10
fi那个set timeout=10，这里面的进行了一个判断，有一个timeout变量，这个变量就是保存系统默认等待时间的变量，这些我们都可以不管，之后将set timeout=10后面的10改成其他的数字，那么系统默认等待时间就会改变了。
因为使用的是ubuntu的grub引导，所以默认启动的系统就是ubuntu，但是这个默认是可以改的：
if [ "${next_entry}" ] ; then
set default="${next_entry}"
set next_entry=
save_env next_entry
set boot_once=true
else
set default="0"
fi
里面有一个set default=”0”，这个0指向的就是ubuntu系统，我们可以更改成为windows对应的数字，也就是windows是第几个引导而已，上面就是我的grub.cfg配置，默认的ubuntu引导