ubuntu 12.04系统EFI启动分区中/EFI/ubuntu/grub.cfg配置文件详解
ubuntu server 12.04 64位系统，安装在gpt分区的硬盘上，第一个分区为 EFI启动分区，挂载点为/boot/efi硬盘各分区UUID为：
root@ubuntu:/boot/efi/EFI/ubuntu# blkid
/dev/sda1: UUID="5FC5-6FEF" TYPE="vfat"
/dev/sda2: UUID="2df31e48-d767-4a42-b0fc-9c2819d886ac" TYPE="ext4"
/dev/sda3: UUID="c5db3401-61aa-4d69-a1f0-33a55206c0c7" TYPE="ext4"
grub.cfg在根目录下的位置：
/boot/efi/EFI/ubuntu/grub.cfg
grub.cfg配置文件内容如下：
search.fs_uuid 2df31e48-d767-4a42-b0fc-9c2819d886ac root
set prefix=($root)/boot/grub
configfile $prefix/grub.cfg
从配置文件中可以看出，启动流程应该是这样的，在启动时先读取/boot/efi/EFI/ubuntu/grub.cfg配置文件，由于此配置文件内嵌了/boot/grub/grub.cfg配置文件，然后再读取/boot/grub/grub.cfg配置文件。
/boot/grub/grub.cfg配置文件如下：
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#
# 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 "${boot_once}" ]; then save_env recordfail; fi; fi
}
function load_video {
insmod efi_gop
insmod efi_uga
insmod video_bochs
insmod video_cirrus
}
insmod part_gpt
insmod ext2
set root='(hd1,gpt2)'
search --no-floppy --fs-uuid --set=root 2df31e48-d767-4a42-b0fc-9c2819d886ac
if loadfont /usr/share/grub/unicode.pf2 ; then
set gfxmode=auto
load_video
insmod gfxterm
insmod part_gpt
insmod ext2
set root='(hd1,gpt2)'
search --no-floppy --fs-uuid --set=root 2df31e48-d767-4a42-b0fc-9c2819d886ac
set locale_dir=($root)/boot/grub/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=hidden
set timeout=0
# Fallback hidden-timeout code in case the timeout_style feature is
# unavailable.
elif sleep --interruptible 0 ; then
set timeout=0
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
### 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 [ ${match} = 0 ]; then
set linux_gfx_mode=keep
else
set linux_gfx_mode=text
fi
else
set linux_gfx_mode=text
fi
else
set linux_gfx_mode=keep
fi
else
set linux_gfx_mode=text
fi
export linux_gfx_mode
if [ "${linux_gfx_mode}" != "text" ]; then load_video; fi
menuentry 'Ubuntu，Linux 3.13.0-92-generic' --class ubuntu --class gnu-linux --class gnu --class os {
recordfail
gfxmode $linux_gfx_mode
insmod gzio
insmod part_gpt
insmod ext2
set root='(hd1,gpt2)'
search --no-floppy --fs-uuid --set=root 2df31e48-d767-4a42-b0fc-9c2819d886ac
linux /boot/vmlinuz-3.13.0-92-generic.efi.signed root=UUID=2df31e48-d767-4a42-b0fc-9c2819d886ac ro quiet splash $vt_handoff
initrd /boot/initrd.img-3.13.0-92-generic
}
menuentry 'Ubuntu, with Linux 3.13.0-92-generic (recovery mode)' --class ubuntu --class gnu-linux --class gnu --class os {
recordfail
insmod gzio
insmod part_gpt
insmod ext2
set root='(hd1,gpt2)'
search --no-floppy --fs-uuid --set=root 2df31e48-d767-4a42-b0fc-9c2819d886ac
echo '载入 Linux 3.13.0-92-generic ...'
linux /boot/vmlinuz-3.13.0-92-generic.efi.signed root=UUID=2df31e48-d767-4a42-b0fc-9c2819d886ac ro recovery nomodeset
echo '载入初始化内存盘...'
initrd /boot/initrd.img-3.13.0-92-generic
}
### END /etc/grub.d/10_linux ###
### BEGIN /etc/grub.d/20_linux_xen ###
### END /etc/grub.d/20_linux_xen ###
### BEGIN /etc/grub.d/20_memtest86+ ###
menuentry "Memory test (memtest86+)" {
insmod part_gpt
insmod ext2
set root='(hd1,gpt2)'
search --no-floppy --fs-uuid --set=root 2df31e48-d767-4a42-b0fc-9c2819d886ac
linux16 /boot/memtest86+.bin
}
menuentry "Memory test (memtest86+, serial console 115200)" {
insmod part_gpt
insmod ext2
set root='(hd1,gpt2)'
search --no-floppy --fs-uuid --set=root 2df31e48-d767-4a42-b0fc-9c2819d886ac
linux16 /boot/memtest86+.bin console=ttyS0,115200n8
}
### END /etc/grub.d/20_memtest86+ ###
### BEGIN /etc/grub.d/30_os-prober ###
### END /etc/grub.d/30_os-prober ###
### BEGIN /etc/grub.d/30_uefi-firmware ###
### END /etc/grub.d/30_uefi-firmware ###
### BEGIN /etc/grub.d/40_custom ###
# This file provides an easy way to add custom menu entries.Simply type the
# menu entries you want to add after this comment.Be careful not to change
# the 'exec tail' line above.
### END /etc/grub.d/40_custom ###
### BEGIN /etc/grub.d/41_custom ###
if [ -f$prefix/custom.cfg ]; then
source $prefix/custom.cfg;
fi
### END /etc/grub.d/41_custom ###
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让ubuntu server 12.04 显示 grub 菜单的方法
默认情况下，如果系统只有一个版本的ubuntu，grub菜单是不显示的。最近由于显示驱动方面的问题，有时候因为花屏导致无法进入系统，一次使用U盘进入，一次是ssh远程进入，为了避免类似尴尬的局面，打算显示grub菜单。
步骤如下：
[*]首先备份/etc/default/grub文件
[*]打开/etc/default/grub文件，找到
[*]GRUB_HIDDEN_TIMEOUT=0
这行，使用#注释掉，变成
[*]#GRUB_HIDDEN_TIMEOUT=0
[*]找到
[*]GRUB_TIMEOUT=10
把10变成3,意思是等待3秒钟。
[*]GRUB_TIMEOUT=3
[*]保存后，执行命令
[*]sudo update-grub
现在启动的时候就会显示grub菜单了，如果3秒内不选择，则会自动进入系统。
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