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翻译中。。。。。
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Grub 2: Heal your bootloader
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================================================================================
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**There are few things as irritating as a broken bootloader. Get the best out of Grub 2 and keep it shipshape.**
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Why do this?
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- Grub 2 is the most popular bootloader that’s used by almost every Linux distribution.
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- A bootloader is a vital piece of software, but they are susceptible to damage.
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- Grub 2 is an expansive and flexible boot loader that offers various customisable options.
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The Grub 2 Linux bootloader is a wonderful and versatile piece of software. While it isn’t the only bootloader out there, it’s the most popular and almost all the leading desktop distros use it. The job of the Grub bootloader is twofold. First, it displays a menu of all installed operating systems on a computer and invites you to pick one. Second, Grub loads the Linux kernel if you choose a Linux operating system from the boot menu.
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As you can see, if you use Linux, you can’t escape the bootloader. Yet it’s one the least understood components inside a Linux distro. In this tutorial we’ll familiarise you with some of Grub 2’s famed versatility and equip you with the skills to help yourself when you have a misbehaving bootloader.
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The most important parts of Grub 2 are a bunch of text files and a couple of scripts. The first piece to know is **/etc/default/grub**. This is the text file in which you can set the general configuration variables and other characteristics of the Grub 2 menu (see box titled “Common user settings”).
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The other important aspect of Grub 2 is the **/etc/grub.d** folder. All the scripts that define each menu entry are housed there. The names of these scripts must have a two-digit numeric prefix. Its purpose is to define the order in which the scripts are executed and the order of the corresponding entries when the Grub 2 menu is built. The **00_header** file is read first, which parses the **/etc/default/grub** configuration file. Then come the entries for the Linux kernels in the **10_linux** file. This script creates one regular and one recovery menu entry for each kernel in the default **/boot** partition.
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This script is followed by others for third-party apps such as **30_os-prober** and **40_custom**. The **os-prober** script creates entries for kernels and other operating systems found on other partitions. It can recognise Linux, Windows, BSD and Mac OS X installations. If your hard disk layout is too exotic for the **os-prober** script to pick up an installed distro, you can add it to the **40_custom** file (see the “Add custom entries” box).
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**Grub** 2 does not require you to manually maintain your boot options’ configuration file: instead it generates the **/boot/grub/grub.cfg** file with the **grub2-mkconfig** command. This utility will parse the scripts in the **/etc/grub.d** directory and the **/etc/default/grub** settings file to define your setup.
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Graphical boot repair
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A vast majority of Grub 2 issues can easily be resolved with the touch of a button thanks to the Boot Repair app. This nifty little application has an intuitive user interface and can scan and comprehend various kinds of disk layouts and partitioning schemes, and can sniff out and correctly identify operating system installations inside them. The utility works on traditional computers with a Master Boot Record (MBR) as well as the newer UEFI computers with the UID Partition Table (GPT) layout.
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The easiest way to use Boot Repair is to install it inside a Live Ubuntu session. Fire up an Ubuntu Live distro on a machine with a broken bootloader and install Boot Repair by first adding its PPA repository with
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sudo add-apt-repository ppa:yannubuntu/Boot Repair
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Then refresh the list of repositories with
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sudo apt-get update
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before installing the app with
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sudo apt-get install -y Boot Repair
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Fire up the tool once it’s installed. The app will scan your hard disk before displaying its interface, which is made up of a couple of buttons. To follow the advice of the tool, simply press the Recommended Repair button, which should fix most broken bootloaders. After it’s restored your bootloader, the tool also spits out a small URL which you should note. The URL contains a detailed summary of your disks, including your partitions along with the contents of important Grub 2 files including **/etc/default/grub** and **boot/grub/grub.cfg**. If the tool hasn’t been able to fix your bootloader, you can share the URL on your distro’s forum boards to allow others to understand your disk layout and offer suggestions.
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**Boot Repair also lets you customise Grub 2’s options.**
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#### Bootloader bailout ####
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Grub 2 boot problems can leave the system in several states. The text on the display where you’d expect the bootloader menu gives an indication of the current state of the system. If the system stops booting at the **grub>** prompt, it means the Grub 2 modules were loaded but it couldn’t find the **grub.cfg** file. This is the full Grub 2 command shell and you can do quite a bit here to help yourself. If you see the **grub rescue>** prompt, it means that the bootloader couldn’t find the Grub 2 modules nor could it find any of your boot files. However, if your screen just displays the word ‘GRUB’, it means the bootloader has failed to find even the most basic information that’s usually contained in the Master Boot Record.
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You can correct these Grub failures either by using a live CD or from Grub 2’s command shell. If you’re lucky and your bootloader drops you at the **grub>** prompt, you have the power of the Grub 2 shell at your disposal to correct any errors.
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The next few commands work with both **grub>** and **grub rescue>**. The **set pager=1** command invokes the pager, which prevents text from scrolling off the screen. You can also use the **ls** command which lists all partitions that Grub sees, like this:
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grub> ls
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(hd0) (hd0,msdos5) (hd0,msdos6) (hd1,msdos1)
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As you can see, the command also lists the partition table scheme along with the partitions.
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You can also use the **ls** command on each partition to find your root filesystem:
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grub> ls (hd0,5)/
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lost+found/ var/ etc/ media/ bin/ initrd.gz
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boot/ dev/ home/ selinux/ srv/ tmp/ vmlinuz
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You can drop the **msdos** bit from the name of the partition. Also, if you miss the trailing slash and instead say **ls (hd0,5)** you’ll get information about the partition including its filesystem type, total size, and last modification time. If you have multiple partitions, read the contents of the **/etc/issue** file with the **cat** command to identify the distro, such as **cat (hd0,5)/etc/issue**.
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Assuming you find the root filesystem you’re looking for inside **(hd0,5)**, make sure that it contains the /**boot/grub** directory and the Linux kernel image you wish to boot into, such as **vmlinuz-3.13.0-24-generic**. Now type the following:
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grub> set root=(hd0,5)
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grub> linux /boot/vmlinuz-3.13.0-24-generic root=/dev/sda5
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grub> initrd /boot/initrd.img-3.13.0-24-generic
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The first command points Grub to the partition housing the distro we wish to boot into. The second command then tells Grub the location of the kernel image inside the partition as well as the location of the root filesystem. The final line sets the location of the initial ramdisk file. You can use tab autocompletion to fill in the name of the kernel and the initrd, which will save you a lot of time and effort.
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Once you’ve keyed these in, type **boot** at the next **grub>** prompt and Grub will boot into the specified operating system.
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Things are a little different if you’re at the **grub rescue>** prompt. Since the bootloader hasn’t been able to find and load any of the required modules, you’ll have to insert them manually:
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grub rescue> set root=(hd0,5)
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grub rescue> insmod (hd0,5)/boot/grub/normal.mod
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grub rescue> normal
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grub> insmod linux
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As you can see, just like before, after we use the **ls** command to hunt down the Linux partition, we mark it with the **set** command. We then insert the **normal** module, which when activated will return us to the standard **grub>** mode. The next command then inserts the linux module in case it hasn’t been loaded. Once this module has been loaded you can proceed to point the boot loader to the kernel image and initrd files just as before and round off the procedure with the **boot** command to bring up the distro.
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Once you’ve successfully booted into the distro, don’t forget to regenerate a new configuration file for Grub with the
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grub-mkconfig -o /boot/grub/grub.cfg
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command. You’ll also have to install a copy of the bootloader into the MBR with the
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sudo grub2-install /dev/sda
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command.
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**To disable a script under the /etc/grub.d, all you need to do is remove the executable bit, for example with chmod -x /etc/grub.d/20_memtest86+ which will remove the ‘Memory Test’ option from the menu.**
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### Grub 2 and UEFI ###
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UEFI-enabled machines (more or less, any machine sold in the last couple of years) have added another layer of complexity to debugging a broken **Grub 2** bootloader. While the procedure for restoring a **Grub 2** install on a UEFI machine isn’t much different than it is on a non-UEFI machine, the newer firmware handles things differently, which results in mixed restoration results.
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On a UEFI-based system, you do not install anything in the MBR. Instead you install a Linux EFI bootloader in the EFI System Partition (ESP) and set it as the EFI’s default boot program using a tool such as **efibootmgr** for Linux, or **bcdedit** for Windows.
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As things stand now, the Grub 2 bootloader should be installed properly when installing any major desktop Linux distro, which will happily coexist with Windows 8. However, if you end up with a broken bootloader, you can restore the machine with a live distro. When you boot the live medium, make sure you boot it in the UEFI mode. The computer’s boot menu will have two boot options for each removable drive – a vanilla option and an option tagged with UEFI. Use the latter to expose the EFI variables in **/sys/firmware/efi/**.
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From the live environment, mount the root filesystem of the broken installation as mentioned in the tutorial. You’ll also have to mount the ESP partition. Assuming it’s **/dev/sda1**, you can mount it with
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sudo mount /dev/sda1 /mnt/boot/efi
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Then load the **efivars** module with **modprobe efivars** before chrooting into the installed distribution as shown in the tutorial.
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Here on, if you’re using Fedora, reinstall the bootloader with the
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yum reinstall grub2-efi shim
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command followed by
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grub2-mkconfig -o /boot/grub2/grub.cfg
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to generate the new configuration file. Ubuntu users can do this with
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apt-get install --reinstall grub-efi-amd64
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With the bootloader in place, exit chroot, unmount all partitions and reboot to the Grub 2 menu.
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#### Dude, where’s my Grub? ####
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The best thing about Grub 2 is that you can reinstall it whenever you want. So if you lose the Grub 2 bootloader, say when another OS like Windows replaces it with its own bootloader, you can restore Grub within a few steps with the help of a live distro. Assuming you’ve installed a distro on **/dev/sda5**, you can reinstall Grub by first creating a mount directory for the distro with
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sudo mkdir -p /mnt/distro
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and then mounting the partition with
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mount /dev/sda5 /mnt/distro
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You can then reinstall Grub with
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grub2-install --root-directory=/mnt/distro /dev/sda
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This command will rewrite the MBR information on the **/dev/sda** device, point to the current Linux installation and rewrite some Grub 2 files such as **grubenv** and **device.map**.
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Another common issue pops up on computers with multiple distros. When you install a new Linux distro, its bootloader should pick up the already installed distros. In case it doesn’t, just boot into the newly installed distro and run
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grub2-mkconfig
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Before running the command, make sure that the root partitions of the distros missing from the boot menu are mounted. If the distro you wish to add has **/root** and **/home** on separate partitions, only mount the partition that contains /root, before running the **grub2-mkconfig** command.
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While Grub 2 will be able to pick most distros, trying to add a Fedora installation from within Ubuntu requires one extra step. If you’ve installed Fedora with its default settings, the distro’s installer would have created LVM partitions. In this case, you’ll first have to install the **lvm2** driver using the distro’s package management system, such as with
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sudo apt-get install lvm2
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before Grub 2’s **os-prober** script can find and add Fedora to the boot menu.
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### Common user settings ###
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Grub 2 has lots of configuration variables. Here are some of the common ones that you’re most likely to modify in the **/etc/default/grub** file. The **GRUB_DEFAULT** variable specifies the default boot entry. It will accept a numeric value such as 0, which denotes the first entry, or “saved” which will point it to the selected option from the previous boot. The **GRUB_TIMEOUT** variable specifies the delay before booting the default menu entry and the **GRUB_CMDLINE_LINUX** variable lists the parameters that are passed on the kernel command line for all Linux menu entries.
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If the **GRUB_DISABLE_RECOVERY** variable is set to **true**, the recovery mode menu entries will not be generated. These entries boot the distro into single-user mode from where you can repair your system with command line tools. Also useful is the **GRUB_GFXMODE** variable, which specifies the resolution of the text shown in the menu. The variable can take any value supported by your graphics card.
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**Grub 2 has a command line, which you can invoke by pressing C at the bootloader menu.**
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#### Thorough fix ####
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If the **grub2-install** command didn’t work for you, and you still can’t boot into Linux, you’ll need to completely reinstall and reconfigure the bootloader. For this task, we’ll use the venerable **chroot** utility to change the run environment from that of the live CD to the Linux install we want to recover. You can use any Linux live CD for this purpose as long as it has the **chroot** tool. However, make sure the live medium is for the same architecture as the architecture of the installation on the hard disk. So if you wish to **chroot** to a 64-bit installation you must use an amd64 live distro.
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After you’ve booted the live distro, the first order of business is to check the partitions on the machine. Use **fdisk -l** to list all the partitions on the disk and make note of the partition that holds the Grub 2 installation that you want to fix.
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Let’s assume we wish to restore the bootloader from the distro installed in **/dev/sda5**. Fire up a terminal and mount it with:
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sudo mount /dev/sda5 /mnt
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Now you’ll have to bind the directories that the Grub 2 bootloader needs access to in order to detect other operating systems:
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$ sudo mount --bind /dev /mnt/dev
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$ sudo mount --bind /dev/pts /mnt/dev/pts
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$ sudo mount --bind /proc /mnt/proc
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$ sudo mount --bind /sys /mnt/sys
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We’re now all set to leave the live environment and enter into the distro installed inside the **/dev/sda5** partition via **chroot**:
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$ sudo chroot /mnt /bin/bash
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You’re now all set to install, check, and update Grub. Just like before, use the
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sudo grub2-install /dev/sda
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command to reinstall the bootloader. Since the **grub2-install** command doesn’t touch the **grub.cfg** file, we’ll have to create it manually with
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sudo grub-mkconfig -o /boot/grub/grub.cfg
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That should do the trick. You now have a fresh copy of Grub 2 with a list of all the operating systems and distros installed on your machine. Before you can restart the computer, you’ll have to exit the chrooted system and unmount all the partitions in the following order:
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$ exit
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$ sudo umount /mnt/sys
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$ sudo umount /mnt/proc
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$ sudo umount /mnt/dev/pts
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$ sudo umount /mnt/dev
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$ sudo umount /mnt
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You can now safely reboot the machine, which should be back under Grub 2’s control, and the bootloader under yours!
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### Add custom entries ###
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If you wish to add an entry to the bootloader menu, you should add a boot stanza to the **40_custom** script. You can, for example, use it to display an entry to boot a Linux distro installed on a removable USB drive. Assuming your USB drive is **sdb1**, and the vmlinuz kernel image and the initrd files are under the root (/) directory, add the following to the **40_custom** file:
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menuentry “Linux on USB” {
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set root=(hd1,1)
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linux /vmlinuz root=/dev/sdb1 ro quiet splash
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initrd /initrd.img
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}
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For more accurate results, instead of device and partition names you can use their UUIDs, such as
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set root=UUID=54f22dd7-eabe
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Use
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sudo blkid
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to find the UUIDs of all the connected drives and partitions. You can also add entries for any distros on your disk that weren’t picked up by the os-prober script, as long as you know where the distro’s installed and the location of its kernel and initrd image files.
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--------------------------------------------------------------------------------
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via: https://www.linuxvoice.com/grub-2-heal-your-bootloader/
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作者：[Mayank Sharma][a]
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译者：[译者ID](https://github.com/译者ID)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]:https://www.linuxvoice.com/author/mayank/
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235
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Grub 2：拯救你的 bootloader
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================================================================================
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**没什么事比 bootloader 坏掉更让气人的了。充分发挥 Grub 2 的作用，让 bootloader 安分工作吧。**
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为什么这么说？
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- Grub 2 是最受欢迎的 bootloader ，受用于几乎所有 Linux 发行版。
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- bootloader 是一个至关重要的软件，但是非常容易损坏。
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- Grub 2 是具有扩展性和灵活性一款引导加载程序，提供了大量可定制选项。
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Grub 2 是一款精彩的功能强大的软件。它不是 bootloader 界一枝独秀，但却最受欢迎，几乎所有主要的桌面发行版都在使用它。 Grub 的工作有两个。首先，它用一个菜单展示计算机上所有已经安装的操作系统供你选择。然后，当你从启动菜单中选择了一个 Linux 操作系统， Grub 便加载这个 Linux 的内核。
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你知道，如果使用 Linux ，你就离不开 bootloader 。然而它却是 Linux 发行版内部最鲜为人知的部分。在这个教程里，我们将带你熟悉 Grub 2 一些著名的特性，强化你相关技能，使你在 bootloader 跑飞的时候能够自行处理。
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Grub 2 最重要的特色在于大量的 text 格式文件和两个脚本文件。首先需要了解的是 **/etc/default/grub** 。这是一个 text 文件，你可以在里面设置通用配置变量和 Grub 2 菜单（见标题为 “Common user settings（普通用户设置）” 的窗口）的其它特性。
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Grub 2 另一个重要的特点在于 **/etc/grub.d** 文件夹。定义菜单入口的所有脚本都放置在这里。这些脚本的名称必须有两位的数字前缀。其目的是，在构建 Grub 2 菜单时定义脚本的执行顺序以及相应入口的顺序。文件 **00_header** 首先被读取，负责解析 **/etc/default/grub** 配置文件。然后是 Linux 内核的入口，位于 **10_linux** 文件中。这个脚本在默认的 **/boot** 分区为每个内核创建一个正规菜单入口和一个恢复菜单入口。
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紧接着的是为第三方应用所用的脚本，如 **30_os-prober** 和 **40_custom** 。 **os-prober** 脚本为内核和其它分区里的操作系统创建入口。它能识别 Linux、 Windows、 BSD 以及 Mac OS X 的装置（译注，指 bootloader ）。 如果你的硬盘设计比较独特，使得 **os-prober** 无法捕获已经安装的发行版，你可以在 **40_custom** 文件（见 “Add custom entries（添加定制入口）”窗口）中添加入口。
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**Grub** 2 不需要你手动维护你的启动选项的配置文件：取而代之的是使用 **grub2-mkconfig** 命令产生 **/boot/grub/grub.cfg** 文件。这个功能会解析 **/etc/grub.d** 目录中的脚本以及 **/etc/default/grub** 设置文件来定义你的安装。
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图形化引导修复
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多亏了 Boot Repair 应用，只需要点击按钮，Grub 2 许许多多的问题都能轻易解决。这个小巧的应用有一个直观的用户界面，可以扫描并包含多种硬盘设计和分区方案，还能发现并正确识别里面的操作系统的装置（译注，指 bootloader ）。这个应用可以以主引导记录 (MBR)形式存在于传统计算机里，也可以在新型 UEFI 计算机中以 GUID（译改，应为GUID）分区表布局方式工作。
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Boot Repair 最简单的使用方式是在 Live Ubuntu 会话中安装。在机器上用一个坏的 bootloader 启动 Ubuntu Live 发行版，通过首次添加它的 PPA 版本库，安装 Boot Repair ，命令如下
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sudo add-apt-repository ppa:yannubuntu/Boot Repair
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然后刷新版本库列表，使用
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sudo apt-get update
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安装应用（译改，删了 before ），如下
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sudo apt-get install -y Boot Repair
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|
||||
安装完毕立刻启动应用。在显示它的界面（由一对按键组成）之前将会扫描你的硬盘。根据工具的指示，只需按下 Recommended Repair（推荐修复）按钮，即可修复大部分坏掉的 bootloader 。修复 bootloader 之后，这个工具会输出一串短小的 URL ，你应该把它记录下来。这个 URL 包含了硬盘详尽的信息：分区信息以及 Grub 2 重要的文件（如 **/etc/default/grub** 和 **boot/grub/grub.cfg** ）的内容。如果工具不能解决 bootloader 的问题，可以把你这个 URL 共享在你的发行版的论坛公告牌上，让其他人分析你的硬盘设计以便给你建议。
|
||||
|
||||
|
||||
|
||||
**Boot Repair 同样支持定制 Grub 2 的选项。**
|
||||
|
||||
#### Bootloader 急救 ####
|
||||
|
||||
Grub 2 引导问题会导致系统处于几种不同状态。屏幕（如你所想，本该显示 bootloader 菜单的地方）所展示的文本，指示系统的当前状态。如果系统中止于 **grub>** 提示符，表明 Grub 2 模块已经被加载，但是找不到 **grub.cfg** 文件。当前是全 Grub 2 命令shell，你可以通过多种方式解决此问题。如果你看到的是 **grub rescue>** 提示符，表明 bootloader 不能找到 Grub 2 模块或者找不到任何引导文件（ boot files ）。然而，如果你的屏幕只显示 ‘GRUB’ 一词，表明 bootloader 找不到通常位于主引导记录（ Master Boot Record ）里的最基本的信息。
|
||||
|
||||
你可以通过使用 live CD 或者在 Grub 2 shell中修正此类错误。如果你够幸运， bootloader 中止于 **grub>** 提示符，你将能获得 Grub 2 shell 的支配权，来帮助你排错。
|
||||
|
||||
接下来几个命令工作在 **grub>** 和 **grub rescue>** 提示符下。 **set pager=1** 命令产生分页器（ pager ），防止文本在屏幕上被刷掉。你还可以使用 **ls** 命令列出 Grub 识别的分区，如下：
|
||||
|
||||
grub> ls
|
||||
(hd0) (hd0,msdos5) (hd0,msdos6) (hd1,msdos1)
|
||||
|
||||
如你所见，这个命令列出分区的同时一并列出了分区表计划。
|
||||
|
||||
你还可以在每个分区上面使用 **ls** 来查找根文件系统：
|
||||
|
||||
grub> ls (hd0,5)/
|
||||
lost+found/ var/ etc/ media/ bin/ initrd.gz
|
||||
boot/ dev/ home/ selinux/ srv/ tmp/ vmlinuz
|
||||
|
||||
你可以不写上分区名的 **msdos** 位。同样，如果你忘记尾斜杠（ the trailing slash ）只输入 **ls (hd0,5)** ，那你将获得分区的信息比如文件系统类型，总体大小和最后修改时间。如果你有多个分区，可以使用 **cat** 读取 **/etc/issue** 文件中的内容，来确定发行版，格式如 **cat (hd0,5)/etc/issue** 。
|
||||
|
||||
假设你在 **(hd0,5)** 中找到根文件系统，请确保它包含 /**boot/grub** 目录，以及你想引导进入的内核镜像，如 **vmlinuz-3.13.0-24-generic** 。此时输入以下命令：
|
||||
|
||||
grub> set root=(hd0,5)
|
||||
grub> linux /boot/vmlinuz-3.13.0-24-generic root=/dev/sda5
|
||||
grub> initrd /boot/initrd.img-3.13.0-24-generic
|
||||
|
||||
第一个命令把 Grub 指向我们想引导进入的发行版所在的分区。接着第二个命令告知 Grub 内核镜像在分区中的位置，以及根文件系统的位置。最后一行设置虚拟文件系统（ initial ramdisk ）文件的位置。你可以使用 tab 补全功能补全内核名字和虚拟文件系统（ initrd: initial ramdisk ）名字，节省时间和精力。
|
||||
|
||||
输入完毕，在下一个 **grub>** 提示符后输入 **boot** ， Grub 将会引导进入指定的操作系统。
|
||||
|
||||
在 **grub rescue>** 提示符下，情况会有些许不同。因为 bootloader 未能够找到并加载任何必需的模块，你需要手动添加这些模块：
|
||||
|
||||
grub rescue> set root=(hd0,5)
|
||||
grub rescue> insmod (hd0,5)/boot/grub/normal.mod
|
||||
grub rescue> normal
|
||||
grub> insmod linux
|
||||
|
||||
如上所示，跟之前一样，使用 **ls** 命令列出所有分区之后，使用 **set** 命令标记起来。然后添加 **normal** 模块，此模块激活时将会恢复标准 **grub>** 模式。如果 linux 模块没加载，接下来的命令会进行添加。如果这个模块已经加载，你可以跟之前一样，把引导加载程序指向内核镜像和虚拟文件系统（ initrd ）文件，然后使用 **boot** 启动发行版，完美收官。
|
||||
|
||||
一旦成功启动发行版，别忘了为 Grub 重新产生新的配置文件，使用
|
||||
|
||||
grub-mkconfig -o /boot/grub/grub.cfg
|
||||
|
||||
命令。你还需要往 MBR 里安装一份 bootloader 的拷贝，使用
|
||||
|
||||
sudo grub2-install /dev/sda
|
||||
|
||||
命令。
|
||||
|
||||
|
||||
|
||||
**想要禁能 /etc/grub.d 目录下的脚本，你只需移除可执行位，比如使用 chmod -x /etc/grub.d/20_memtest86+ 就能将 ‘Memory Test’ 选项从菜单中移除。**
|
||||
|
||||
### Grub 2 和 UEFI ###
|
||||
|
||||
支持UEFI的机器（最近几年上市的机器大部分都是）添加了另一复杂的层次，用以调试坏掉的 **Grub 2**。恢复 **Grub 2** 的程序在 UEFI 机器上安装和在非 UEFI 机器上安装并没多大区别，只是新程序处理方式不一样，从而导致了很多种恢复结果。
|
||||
|
||||
对于基于 UEFI 的系统，不要在 MBR上安装任何东西。相反，你要在 EFI 系统分区（ ESP ）里安装 EFI bootloader，并且借助工具把它设置为 EFI 的默认启动程序，这个工具对于 Linux 用户是 **efibootmgr** ，对于 window 用户则是 **bcdedit** 。
|
||||
|
||||
照目前情况看，在安装任何与 Windows 8 兼容的主流桌面 Linux 发行版前， Grub 2 应该完成正确安装。然而，如果 bootloader 损坏，你可以使用 live 发行版进行机器修复。在启动 live 媒介之时，请确保是以 UEFI模式启动。计算机每个可移动驱动的启动菜单将会有两个选项： vanilla 选项和以 EFI 标记的选项。使用后者开放 **/sys/firmware/efi/** 文件中的 EFI 变量。
|
||||
|
||||
在 live 环境中，挂载教程前面所提的安装失败的装置（译注，指 bootloader ）的根文件系统。除此之外，还需要挂载 ESP 分区。假设分区是 **/dev/sda1** ，你可以如下所示挂载
|
||||
|
||||
sudo mount /dev/sda1 /mnt/boot/efi
|
||||
|
||||
接着在 chroot 到安装完毕的发行版前之前，使用 **modprobe efivars** 加载 **efivars** 模块。
|
||||
|
||||
这个时候， Fedora 用户使用如下命令重新安装 bootloader
|
||||
|
||||
yum reinstall grub2-efi shim
|
||||
|
||||
在此之前，需要使用
|
||||
|
||||
grub2-mkconfig -o /boot/grub2/grub.cfg
|
||||
|
||||
来产生新的配置文件。 Ubuntu 用户则改用以下命令
|
||||
|
||||
apt-get install --reinstall grub-efi-amd64
|
||||
|
||||
一旦 bootloader 正确就位，退出 chroot ，取消挂载所有分区，重启让 Grub 2 菜单显示。
|
||||
|
||||
#### 伙计，我的 Grub 哪去了？ ####
|
||||
|
||||
Grub 2 最好的特性是可以随时重新安装。因此，当其它像 Windows 之类的系统用自己的 bootloader 替换之，导致 Grub 2 丢失，你可以使用 live 发行版，寥寥数步即可重装 Grub 。假设你在 **/dev/sda5** 安装了一个发行版，若要重装 Grub ，你只需首先使用以下命令，为发行版创建一个挂载目录
|
||||
|
||||
sudo mkdir -p /mnt/distro
|
||||
|
||||
然后挂载分区，如下
|
||||
|
||||
mount /dev/sda5 /mnt/distro
|
||||
|
||||
接着就能重装 Grub 了，如下
|
||||
|
||||
grub2-install --root-directory=/mnt/distro /dev/sda
|
||||
|
||||
这个命令会改写 **/dev/sda** 设备上的 MBR 信息，指向当前 Linux 的装置（译注，指 bootloader ），并改写 Grub 2 部分文件如 **grubenv** 和 **device.map** 。
|
||||
|
||||
另一个问题常见于装有多个发行版的计算机上。安装了新的 Linux 发行版，它的 bootloader 应当要能捕获所有已经安装的发行版。一旦不能够，只要引导进入新安装的发行版，并运行
|
||||
|
||||
grub2-mkconfig
|
||||
|
||||
运行命令之前，请确保发行版的启动菜单中缺失的 root 分区已经完成挂载。如果你想添加的发行版有独立 **/root** 和 **/home** 分区，在运行 **grub2-mkconfig** 之前，只需挂载包含 /root 的分区。
|
||||
|
||||
虽然 Grub 2 能够捕获大部分发行版，但是在 Ubuntu 中尝试添加 Fedora 的装置（译注，指 bootloader ）需要额外的一个步骤。如果你以默认设置安装了 Fedora ，则发行版的安装器（译注，同样指 bootloader ）已经创建了 LVM 分区。此时你需要使用发行版的包管理系统，安装 **lvm2** 驱动，如下
|
||||
|
||||
sudo apt-get install lvm2
|
||||
|
||||
才能使得 Grub 2 的 **os-prober** 脚本能够找到并将 Fedora 添加进启动菜单。
|
||||
|
||||
### 普通用户设置 ###
|
||||
|
||||
Grub 2 有很多可配置变量。 **/etc/default/grub** 文件里有很多你最可能会修改到的普通变量。 **GRUB_DEFAULT** 变量指定默认的启动入口，可以设置为数字值，比如 0 ，表示第一个入口，或者设置为 “saved” ，将它从指向上一次启动时选中的选项。 **GRUB_TIMEOUT** 变量指定启动默认菜单入口之前的停留时间。 **GRUB_CMDLINE_LINUX** 为所有 Linux 菜单入口列出在内核命令行上传递的参数。
|
||||
|
||||
如果 **GRUB_DISABLE_RECOVERY** 变量设置为 **true** ，那么将不产生恢复模式菜单入口。这些入口以单用户模式启动发行版，这种模式下允许你利用命令行工具修复系统。 **GRUB_GFXMODE** 变量同样有用，它指定了菜单上文本显示的分辨率，它可以设置为你的显卡所支持的任何数值。
|
||||
|
||||
|
||||
|
||||
** Grub 2 有其命令行，通过在 bootloader 菜单上按 C 调用。**
|
||||
|
||||
#### 彻底的修复 ####
|
||||
|
||||
如果 **grub2-install** 命令不能正常运作，使得你无法引导进入 Linux ，你需要完整地重装以及重新配置 bootloader 。为此目的，需要用到神圣的 **chroot** 应用将 live CD 环境切换至并运行我们想修复的 Linux 的安装环境。任何拥有 **chroot** 工具的 Linux live CD 都可以实现这个目的。不过需要确保 live 媒介的架构和硬盘上系统的架构一致。因此当你希望 **chroot** 到 64 位系统，你必须使用 amd64 live 发行版。
|
||||
|
||||
启动进入 live 发行版之后，首先需要检查机器上的分区。使用 **fdisk -l** 列出磁盘上所有分区，记录你想修复的 Grub 2 装置所在的分区。
|
||||
|
||||
假设我们希望从安装在 **/dev/sda5** 中的发行版中恢复 bootloader 。启动终端使用如下命令挂载分区：
|
||||
|
||||
sudo mount /dev/sda5 /mnt
|
||||
|
||||
此时需要绑定 Grub 2 bootloader 需要进入的目录，以便检测其它操作系统：
|
||||
|
||||
$ sudo mount --bind /dev /mnt/dev
|
||||
$ sudo mount --bind /dev/pts /mnt/dev/pts
|
||||
$ sudo mount --bind /proc /mnt/proc
|
||||
$ sudo mount --bind /sys /mnt/sys
|
||||
|
||||
此时可以离开 live 环境进入安装在 **/dev/sda5** 分区中的发行版了，通过 **chroot** ：
|
||||
|
||||
$ sudo chroot /mnt /bin/bash
|
||||
|
||||
现在可以安装、检测、以及升级 Grub 了，跟之前一样，使用
|
||||
|
||||
sudo grub2-install /dev/sda
|
||||
|
||||
命令来重装 bootloader 。因为 **grub2-install** 命令不能 创建**grub.cfg** 文件，需要手动创建，如下
|
||||
|
||||
sudo grub-mkconfig -o /boot/grub/grub.cfg
|
||||
|
||||
这样应该就可以了。现在你就有了 Grub 2 的一份全新拷贝，罗列机器上所有的操作系统和发行版。在重启电脑之前，你需要依次退出 chroot 系统，卸载所有分区，如下所示：
|
||||
|
||||
$ exit
|
||||
$ sudo umount /mnt/sys
|
||||
$ sudo umount /mnt/proc
|
||||
$ sudo umount /mnt/dev/pts
|
||||
$ sudo umount /mnt/dev
|
||||
$ sudo umount /mnt
|
||||
|
||||
现在你可以安全地重启电脑了，而它应该会回退到 Grub 2 的控制之中，而你又控制着这个 bootloader 。
|
||||
|
||||
### 添加自定义入口 ###
|
||||
|
||||
如果希望往 bootloader 菜单里添加入口，你需要在 **40_custom** 文件里添加一个启动段（ boot stanza ）。例如，你可以使用它展示一个入口来启动安装在可移动 USB 驱动里的 Linux 发行版。假设你的 USB 驱动是 **sdb1** ，并且 vmlinuz 内核镜像和虚拟文件系统（ initrd ）都位于根 (/)目录下，在 **40_custom** 文件中添加以下内容：
|
||||
|
||||
menuentry “Linux on USB” {
|
||||
set root=(hd1,1)
|
||||
linux /vmlinuz root=/dev/sdb1 ro quiet splash
|
||||
initrd /initrd.img
|
||||
}
|
||||
|
||||
相比使用设备和分区名，使用它们的 UUID 可以获得更精确结果，比如
|
||||
|
||||
set root=UUID=54f22dd7-eabe
|
||||
|
||||
使用
|
||||
|
||||
sudo blkid
|
||||
|
||||
来获得所有已连接驱动和分区的 UUID 。你还可以为你磁盘上没被 os-prober 脚本捕获的发行版添加入口，只要你知道该发行版的安装位置以及其内核和虚拟文件系统（ initrd ）的定位即可。
|
||||
|
||||
--------------------------------------------------------------------------------
|
||||
|
||||
via: https://www.linuxvoice.com/grub-2-heal-your-bootloader/
|
||||
|
||||
作者：[Mayank Sharma][a]
|
||||
译者：[soooogreen](https://github.com/soooogreen)
|
||||
校对：[校对者ID](https://github.com/校对者ID)
|
||||
|
||||
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
|
||||
|
||||
[a]:https://www.linuxvoice.com/author/mayank/
|
||||
Loading…
Reference in New Issue
Block a user