ubnutu9.10用的GRUB2来引导系统，不幸我弄坏了两次
假如你的ubuntu的 / 分区是 sda7 又假如 /boot分区是 sda6，用livecd启动，在终端下输入

sudo -i

mount /dev/sda7 /mnt

mount /dev/sda6 /mnt/boot （如果没 /boot 单独分区这步跳过）

grub-install --root-directory=/mnt/ /dev/sda

exit

重启

查找grub所在的分区，ubuntu没有另外建分区是在/boot/grub文件夹
> ls
(hd0),(hd0,gt1),(hd1,gt2),(hd1,gt3) and so on
> ls (hdN,msdosX)/boot/grub #顺序查找，直到找到
以(hd0,gt1)

>set root=(hd0,gt1)
>set prefix=(hd0,gt1)/boot/grub
>insmod normal
>normal
这样就可以进入图形化界面了，但是每次重启都又重新出现grub界面； 所以进入界面后，需要操作：
>sudo update-grub
>sudo grub-install /dev/sda
按照晚上大部分教程，到这一步就可以重启万事大吉了，但是你也可能会出现sudo grub-install /dev/sda 这步骤报错了。。。
Installing for i386-pc platform.
grub-install: warning: this GPT partition label contains no BIOS Boot Partition; embedding won't be possible.
grub-install: error: embedding is not possible, but this is required for cross-disk install.
这个时候输入：
>sudo parted /dev/sda set 1 bios_grub on
>sudo parted /dev/sda print
>sudo grub-install /dev/sda
这样既可成功。如果还是有问题，例如多块硬盘的时候，需要在BIOS里改变启动顺序既可。

一、首先为U盘安装Grub

---

1.
有一款软件叫Gurb-install,下载下来装到U盘即可

2. 现在grub4Dos，仅仅使用其中grldr文件


二、从ubuntu*.iso的casper文件夹中拷贝出vmlinuz、和initrd.gz。将这3个文件(包含原iso文件)放到某个盘的根目录下，比如E盘(hd1,5);


三、使用其中的命令行，进入Grub命令环境

---

root (hd1,5)

kernel /vmlinuz boot=casper
iso-scan/filename=/ubuntu-10.10-desktop-i386.iso

initrd /initrd.lz
 
四、正常启动后最好先执行如下代码：
sudo umount -l /isodevice

来卸载iso分区以便可以正确对磁盘重新分区安装







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ubuntu 10.04 grub2

Ubuntu 10.04 
LTS终于发布了，原来打算过一阵子再把9.10升一下的，但今天在update 
manager里，看到已经有提示说可以直接升到10.04，一时冲动没忍住，于是就升了，接着就碰到魔鬼了：重启后在grub那步出错，过不去了，提示
“GRUB loading error: the symbol  ‘grub_puts_’ not found”，光标就停在grub 
rescue>后面，google找了一些文章，发现国内的几个都大同小异，后面有一些步骤根本没有交代清除，做到一半就进行不下去了，后来找到一
个老外的帖子, 一步一步都很清楚，照着做下来，成功地把grub2修复了。
Boot to the LiveCD Desktop (Ubuntu 9.10 or Ubuntu 10.04).
Open a terminal – Applications, Accessories, Terminal
.
Determine your normal system partition – (the switch is a lowercase 
 “L”) sudo fdisk -l


If you aren’t sure, rundf -Th

. Look for  
the correct disk size and ext3 or ext4 format.

Mount your normal system partition:
Substitute the correct partition: sda1, sdb5, etc.
sudo mount /dev/sdXX /mnt

 # Example: sudo
  mount /dev/sda1 /mnt



Only if you have a separate boot partition
:
sdYY is the /boot partition designation (examply sdb3)
sudo mount /dev/sdYY /mnt/boot



Mount devices:sudo mount --bind /dev/ /mnt/dev


To ensure that only the grub utilities from the LiveCD get executed,
  mount /usrsudo mount --bind /usr/ /mnt/usr


mount proc filesystemsudo mount --bind /proc/ /mnt/proc


Chroot into your normal system device:sudo chroot /mnt


If there is no /boot/grub/grub.cfg or it’s not correct, create one  
usingupdate-grub


Reinstall GRUB 2:
Substitute the correct device – sda, sdb, etc. Do not
 
specify a partition number.
grub-install /dev/sdX



Verify the install (use the correct device, for example sda
.
  Do not
 specify a partition):  sudo grub-install  
--recheck /dev/sdX


Exit chroot
:  CTRL-D
 on keyboard
Unmount devices:sudo umount /mnt/dev


If you mounted a separate /boot partition:sudo umount  
/mnt/boot



Unmount last device:sudo umount /mnt


Reboot.reboot


Post-Restoration Commands
Once the user can boot to a working system, try to determine why the 
 system failed to boot. The following commands may prove useful in  
locating and/or fixing the problem.
To refresh the available devices and settings in /boot/grub/grub.cfg

sudo update-grub


To look for the bootloader location.
grub-probe -t device /boot/grub


To install GRUB 2 to the sdX
 partition’s MBR  (sda, sdb,  
etc.)
sudo grub-install /dev/sdX


To recheck the installation. (sda, sdb, etc.) sudo  
grub-install --recheck /dev/sdX


Please check the following link for further details.


https://help.ubuntu.com/community/Grub2#Reinstalling%20GRUB%202