Use a USB flash drive to install CentOS and write the boot on the USB flash drive. I found that I am a genius! Let's review the scenario: there is an old machine in the company. My colleague said it was okay to study how to install a Linux. I just downloaded a CentOS6.4 a few days ago, and I just completed the work. Unfortunately, the broken machine does not have an optical drive. You have to use a USB flash drive. I won't talk about how to create a boot disk, or how to install it. What I want to say is that I have installed it successfully. (I have a lot of nonsense) The problem is coming. I unplugged the USB flash drive after I restarted it. Then you can't get up again .. I am not so worried. I have a dead heart. It takes me more than an hour to install the system because it is slow to break the machine. I checked it hundreds of times and said it was to install the boot into the USB flash drive. I tried it and the USB flash drive can be started. Miserable. If I had my own computer, I would be too lazy, but this is the company's. You can't always plug in my USB flash drive. So I asked a lot of people in the group and told me to reinstall the system. But I don't have to worry about it. Can I reload it without moving? No worries. The following is a solution. Please refer to the materials of many people! 1. Insert a USB flash drive to enable the system. (If the USB flash drive is swallowed up, you can launch a Live CD.) 2. open a terminal and run the $ sudo grub command (this may take a while). You will see a prompt like 'grub> '3. enter find/grub/stage1 after the prompt 'grub> '. You will get a running result. For example, the result on my machine is (hd0, 0) (This command is actually used to find the partition where/boot is located.) 4. run grub> root (hd0, 0) (enter the running result on your machine. run grub> setup (hd0) and several lines of text are displayed. Succeeded "fixed successfully! 6. Run quit. 7. Run reboot to restart the computer. I am in the mood. It seems like a flower, because I saw the grub startup interface, but I am not happy later. It is restarting, but it still cannot enter the system. Later, I studied the startup items of grub and found a problem. I clearly wrote root (hd0, 0). Why does it become root (hd1, 0? (This is probably a BUG of grub in CentOS6.4 .) Then I press the 'E' key and edit it as root (hd0, 0) to start it. Then how wonderful the world is. Started successfully. After some suffering, I finally don't need to reinstall the system! Finally, I used grub to temporarily Change 1 to 0. In fact, it was not changed at the next startup, but it was still 1. Then I edit the/boot/grub/menu. lst file and change the content to the correct one. Save and exit. Restart. Then the problem is solved. I hope that my experience will help people who encounter the same difficulties as me! The first blog post is a bit nonsense. Thank you for your understanding!