用宿主系统grub引导LFS

如果按照LFS Book使用gurb的做法做，LFS的grub会覆盖原来系统的grub，有可能失去对原来系统的引导。

这方法应该对Gentoo有效，没做过，不太清楚。

笔者本来是Windows7+ubuntu11.04系统，grub内容如下：

/boot/grub/grub.cfg

#
# 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 $prefix/grubenv ]; then
  set have_grubenv=true
  load_env
fi
set default="0"
if [ "${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 {
  insmod vbe
  insmod vga
  insmod video_bochs
  insmod video_cirrus
}

insmod part_msdos
insmod ext2
set root='(hd0,msdos9)'
search --no-floppy --fs-uuid --set=root 17984c85-e681-4de0-adab-bed448e4eae0
if loadfont /usr/share/grub/unicode.pf2 ; then
  set gfxmode=auto
  load_video
  insmod gfxterm
  insmod part_msdos
  insmod ext2
  set root='(hd0,msdos9)'
  search --no-floppy --fs-uuid --set=root 17984c85-e681-4de0-adab-bed448e4eae0
  set locale_dir=($root)/boot/grub/locale
  set lang=zh_CN
  insmod gettext
fi
terminal_output gfxterm
if [ "${recordfail}" = 1 ]; then
  set timeout=-1
else
  set timeout=10
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; then
  clear
fi
### END /etc/grub.d/05_debian_theme ###

### BEGIN /etc/grub.d/10_linux ###
if [ ${recordfail} != 1 ]; then
  if [ -e ${prefix}/gfxblacklist.txt ]; then
    if hwmatch ${prefix}/gfxblacklist.txt 3; then
      if [ ${match} = 0 ]; then
        set linux_gfx_mode=keep
      else
        set linux_gfx_mode=text
      fi
    else
      set linux_gfx_mode=text
    fi
  else
    set linux_gfx_mode=keep
  fi
else
  set linux_gfx_mode=text
fi
export linux_gfx_mode
if [ "$linux_gfx_mode" != "text" ]; then load_video; fi
menuentry 'Ubuntu，Linux 3.0.0-16-generic' --class ubuntu --class gnu-linux --class gnu --class os {
    recordfail
    set gfxpayload=$linux_gfx_mode
    insmod gzio
    insmod part_msdos
    insmod ext2
    set root='(hd0,msdos9)'
    search --no-floppy --fs-uuid --set=root 17984c85-e681-4de0-adab-bed448e4eae0
    linux    /boot/vmlinuz-3.0.0-16-generic root=UUID=17984c85-e681-4de0-adab-bed448e4eae0 ro   quiet splash vt.handoff=7
    initrd    /boot/initrd.img-3.0.0-16-generic
}
menuentry 'Ubuntu，Linux 3.0.0-16-generic (恢复模式)' --class ubuntu --class gnu-linux --class gnu --class os {
    recordfail
    insmod gzio
    insmod part_msdos
    insmod ext2
    set root='(hd0,msdos9)'
    search --no-floppy --fs-uuid --set=root 17984c85-e681-4de0-adab-bed448e4eae0
    echo    '载入 Linux 3.0.0-16-generic ...'
    linux    /boot/vmlinuz-3.0.0-16-generic root=UUID=17984c85-e681-4de0-adab-bed448e4eae0 ro recovery nomodeset 
    echo    '载入初始化内存盘...'
    initrd    /boot/initrd.img-3.0.0-16-generic
}
submenu "Previous Linux versions" {
menuentry 'Ubuntu，Linux 3.0.0-12-generic' --class ubuntu --class gnu-linux --class gnu --class os {
    recordfail
    set gfxpayload=$linux_gfx_mode
    insmod gzio
    insmod part_msdos
    insmod ext2
    set root='(hd0,msdos9)'
    search --no-floppy --fs-uuid --set=root 17984c85-e681-4de0-adab-bed448e4eae0
    linux    /boot/vmlinuz-3.0.0-12-generic root=UUID=17984c85-e681-4de0-adab-bed448e4eae0 ro   quiet splash vt.handoff=7
    initrd    /boot/initrd.img-3.0.0-12-generic
}
menuentry 'Ubuntu，Linux 3.0.0-12-generic (恢复模式)' --class ubuntu --class gnu-linux --class gnu --class os {
    recordfail
    insmod gzio
    insmod part_msdos
    insmod ext2
    set root='(hd0,msdos9)'
    search --no-floppy --fs-uuid --set=root 17984c85-e681-4de0-adab-bed448e4eae0
    echo    '载入 Linux 3.0.0-12-generic ...'
    linux    /boot/vmlinuz-3.0.0-12-generic root=UUID=17984c85-e681-4de0-adab-bed448e4eae0 ro recovery nomodeset 
    echo    '载入初始化内存盘...'
    initrd    /boot/initrd.img-3.0.0-12-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+ ###
menuentry "Memory test (memtest86+)" {
    insmod part_msdos
    insmod ext2
    set root='(hd0,msdos9)'
    search --no-floppy --fs-uuid --set=root 17984c85-e681-4de0-adab-bed448e4eae0
    linux16    /boot/memtest86+.bin
}
menuentry "Memory test (memtest86+, serial console 115200)" {
    insmod part_msdos
    insmod ext2
    set root='(hd0,msdos9)'
    search --no-floppy --fs-uuid --set=root 17984c85-e681-4de0-adab-bed448e4eae0
    linux16    /boot/memtest86+.bin console=ttyS0,115200n8
}
### END /etc/grub.d/20_memtest86+ ###

### BEGIN /etc/grub.d/30_os-prober ###
menuentry "Windows 7 (loader) (on /dev/sda1)" --class windows --class os {
    insmod part_msdos
    insmod ntfs
    set root='(hd0,msdos1)'
    search --no-floppy --fs-uuid --set=root F22A8D3E2A8D00B9
    chainloader +1
}
### END /etc/grub.d/30_os-prober ###

### 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  $prefix/custom.cfg ]; then
  source $prefix/custom.cfg;
fi
### END /etc/grub.d/41_custom ###

电脑启动后会读取grub.cfg文件并显示grub菜单，注意，一个menuentry就是一个菜单项，一个submenu就是一个包含子菜单的菜单项，它们的内容都被“{}”括起来的内容，修改grub文件时，切记不能乱嵌套"{}",切记不能交叉嵌套。

请完整看接下来的一段话，并理解它：

我们的任务是，根据LFS book的步骤，在LFS系统（chroot后）中生成/boot/grub/grub.cfg，只做生成grub的操作而不更新主引导记录（更新的话就覆盖了原来的grub）。然后把新生成的grub.cfg中的LFS启动项添加到宿主系统grub.cfg文件中。

按照LFS book中第八章《使用Grub配置启动过程》的步骤做如下操作（假设你已经做完前面所有的工作，包括安装grub）

注意：这是在chroot环境下的操作：

1、讲grub文件安装到/boot/grub:

grub-install --grub-setup=/bin/true /dev/sda

2、生成/boot/grub/grub.cfg

grub-mkconfig -o /boot/grub/grub.cfg

测试grub你可以自己做也可以不做，到这里停住，不能执行更新主引导记录的操作。

打开一个新的终端，并用gedit打开刚生成的grub.cfg文件。

sudo gedit /mnt/lfs/boot/grub/grub.cfg

我的内容如下：

#
# 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 $prefix/grubenv ]; then
  load_env
fi
set default="0"
if [ "${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 load_video {
  insmod vbe
  insmod vga
  insmod video_bochs
  insmod video_cirrus
}

set timeout=5
### END /etc/grub.d/00_header ###

### BEGIN /etc/grub.d/10_linux ###
menuentry 'GNU/Linux, with Linux 3.2.6-lfs-7.1' --class gnu-linux --class gnu --class os {
    load_video
    insmod gzio
    insmod part_msdos
    insmod ext2
    set root='(hd0,msdos6)'
    search --no-floppy --fs-uuid --set=root d05c4b59-a4b3-4466-9ed4-4f13fd84d8f1
    echo    'Loading Linux 3.2.6-lfs-7.1 ...'
    linux    /boot/vmlinuz-3.2.6-lfs-7.1 root=/dev/sda6 ro  
}
menuentry 'GNU/Linux, with Linux 3.2.6-lfs-7.1 (recovery mode)' --class gnu-linux --class gnu --class os {
    load_video
    insmod gzio
    insmod part_msdos
    insmod ext2
    set root='(hd0,msdos6)'
    search --no-floppy --fs-uuid --set=root d05c4b59-a4b3-4466-9ed4-4f13fd84d8f1
    echo    'Loading Linux 3.2.6-lfs-7.1 ...'
    linux    /boot/vmlinuz-3.2.6-lfs-7.1 root=/dev/sda6 ro single 
}
### END /etc/grub.d/10_linux ###

### BEGIN /etc/grub.d/20_linux_xen ###
### END /etc/grub.d/20_linux_xen ###

### BEGIN /etc/grub.d/30_os-prober ###
### END /etc/grub.d/30_os-prober ###

### 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  $prefix/custom.cfg ]; then
  source $prefix/custom.cfg;
fi
### END /etc/grub.d/41_custom ###

其他不管，找到并复制两个（或一个）LFS的menuentry。我的如下：

menuentry 'GNU/Linux, with Linux 3.2.6-lfs-7.1' --class gnu-linux --class gnu --class os {
    load_video
    insmod gzio
    insmod part_msdos
    insmod ext2
    set root='(hd0,msdos6)'
    search --no-floppy --fs-uuid --set=root d05c4b59-a4b3-4466-9ed4-4f13fd84d8f1
    echo    'Loading Linux 3.2.6-lfs-7.1 ...'
    linux    /boot/vmlinuz-3.2.6-lfs-7.1 root=/dev/sda6 ro  
}
menuentry 'GNU/Linux, with Linux 3.2.6-lfs-7.1 (recovery mode)' --class gnu-linux --class gnu --class os {
    load_video
    insmod gzio
    insmod part_msdos
    insmod ext2
    set root='(hd0,msdos6)'
    search --no-floppy --fs-uuid --set=root d05c4b59-a4b3-4466-9ed4-4f13fd84d8f1
    echo    'Loading Linux 3.2.6-lfs-7.1 ...'
    linux    /boot/vmlinuz-3.2.6-lfs-7.1 root=/dev/sda6 ro single 
}

复制menuentry后，关闭gedit窗口。

打开宿主系统grub文件：

sudo gedit /boot/grub/grub.cfg

把刚复制的内容粘帖到你想要的位置，注意不要乱嵌套。

保存。

OK。正确的话，重启后你原来的grub菜单会多出LFS的启动项。如果引导失败，那很有可能是因为粘帖LFS的menuentry时嵌套到其他系统的menuentry里去了，准备好修复吧。