【Linux使用】Centos 7 GRUB与内核版本切换

妖狐艹你老母 2022-01-28 23:23 739阅读 0赞

### 文章目录 ###

*  系统信息参考
 *  GRUB的配置文件
 *  查找grub.cfg文件
 *  列出所有的引导入口
 *  列出默认的引导入口
 *  修改默认的引导入口
 *  /etc/default/grub文件
 *  重新生成/etc/default/grub文件
 *  打印出所有安装的内核
 *  删除指定的内核

# 系统信息参考 #

[tony@tony-dev ~]$ cat /etc/redhat-release
    CentOS Linux release 7.6.1810 (Core)

# GRUB的配置文件 #

在启用了UEFI的系统上，CentOS 7的GRUB的有效配置文件是 /boot/efi/EFI/centos/grub.cfg。/boot/grub与/boot/grub2目录下已经不再保存配置文件 （参看后图）。

查看一下这个文件的头部说明，可以看到 “不可编辑这个文件”的警告信息，同时指明了修改这个文件的方法：即需要修改/etc/default/grub配置文件与/etc/grub.d目录下的模板后，再用grub2-mkconfig命令生成这个文件。

> \[root@tony-dev boot\]\# sudo cat /boot/efi/EFI/centos/grub.cfg  
> \#  
> \# DO NOT EDIT THIS FILE  
> \#  
> \# It is automatically generated by grub2-mkconfig using templates  
> \# from /etc/grub.d and settings from /etc/default/grub  
> \#

# /boot目录结构图
    [root@tony-dev boot]# tree -F /boot
    /boot
    ├── config-3.10.0-693.11.6.el7.x86_64
        ...
    ├── efi/
    │   └── EFI/
    │       ├── BOOT/
    │       │   ├── BOOTX64.EFI*
    │       │   ├── fallback.efi*
    │       │   └── fbx64.efi*
    │       └── centos/
    │           ├── BOOT.CSV*
    │           ├── BOOTX64.CSV*
    │           ├── fonts/
    │           │   └── unicode.pf2*
    │           ├── fw/
    │           ├── fwupia32.efi*
    │           ├── fwupx64.efi*
    │           ├── grub.cfg*
    │           ├── grub.cfg.1554740803.rpmsave*
    │           ├── grubenv*
    │           ├── grubx64.efi*
    │           ├── mmx64.efi*
    │           ├── MokManager.efi*
    │           ├── shim.efi*
    │           ├── shimx64-centos.efi*
    │           └── shimx64.efi*
    ├── grub/
    │   └── splash.xpm.gz
    ├── grub2/
    │   └── grubenv -> ../efi/EFI/centos/grubenv*
    ├── initramfs-0-rescue-2282c2e0651e46f796865aaa645ac7fe.img
        ...
    ├── lost+found/
    ├── symvers-3.10.0-693.11.6.el7.x86_64.gz
        ...
    ├── vmlinuz-0-rescue-2282c2e0651e46f796865aaa645ac7fe*
        ...
    └── vmlinuz-3.10.0-957.10.1.el7.x86_64.debug*
    
    9 directories, 56 files

# 查找grub.cfg文件 #

# 通常会打印出
    # /boot/efi/EFI/centos/grub.cfg (UEFI-based system)
    # 或者
    # /boot/grub2/grub.cfg (Legacy system)
    
    [tony@tony-dev ~]$ sudo find /boot -name grub.cfg
    /boot/efi/EFI/centos/grub.cfg

# 列出所有的引导入口 #

# 用单引号(')作分隔符，第一个域是"menuentry "的行，就是引导入口。
    [root@tony-dev default]# awk -F\' '$1=="menuentry " {print i++ " : " $2}' $(find /boot -name grub.cfg)
    0 : CentOS Linux (3.10.0-957.10.1.el7.x86_64.debug) 7 (Core)
    1 : CentOS Linux (3.10.0-957.10.1.el7.x86_64) 7 (Core)
    2 : CentOS Linux (3.10.0-693.11.6.el7.x86_64) 7 (Core)
    3 : CentOS Linux (3.10.0-693.el7.centos.tony_base.x86_64.debug) 7 (Core)
    4 : CentOS Linux (3.10.0-693.el7.centos.tony_base.x86_64) 7 (Core)
    5 : CentOS Linux (3.10.0-693.el7.x86_64) 7 (Core)
    6 : CentOS Linux (0-rescue-2282c2e0651e46f796865aaa645ac7fe) 7 (Core)

# 列出默认的引导入口 #

[root@tony-dev default]# grub2-editenv list
    saved_entry=CentOS Linux (3.10.0-957.10.1.el7.x86_64) 7 (Core)

# 修改默认的引导入口 #

[root@tony-dev default]# grub2-set-default 2
    [root@tony-dev default]# grub2-editenv list
    saved_entry=2

# /etc/default/grub文件 #

默认的/etc/default/grub文件并不长，内容如下：

[root@tony-dev default]# cat /etc/default/grub

> GRUB\_TIMEOUT=5  
> GRUB\_DISTRIBUTOR="$(sed ‘s, release .\*$,g’ /etc/system-release)"  
> GRUB\_DEFAULT=saved  
> GRUB\_DISABLE\_SUBMENU=true  
> GRUB\_TERMINAL\_OUTPUT=“console”  
> GRUB\_CMDLINE\_LINUX=“crashkernel=auto rhgb quiet”  
> GRUB\_DISABLE\_RECOVERY=“true”

# 重新生成/etc/default/grub文件 #

修改配置文件后，需要使用如下命令重新生成grub.cfg文件，以使配置文件生效。

grub2-mkconfig -o $(find /boot -name grub.cfg)

# 打印出所有安装的内核 #

[tony@tony-dev ~]$ sudo rpm -q kernel
    kernel-3.10.0-693.el7.x86_64
    kernel-3.10.0-693.el7.centos.tony_base.x86_64
    kernel-3.10.0-693.11.6.el7.x86_64
    kernel-3.10.0-957.10.1.el7.x86_64

# 删除指定的内核 #

[root@tony-dev boot]# sudo yum remove kernel-3.10.0-693.el7.centos.tony_base.x86_64

> Loaded plugins: fastestmirror, langpacks  
> Resolving Dependencies  
> –> Running transaction check  
> —> Package kernel.x86\_64 0:3.10.0-693.el7.centos.tony\_base will be erased  
> –> Finished Dependency Resolution  
> &npsb;  
> Dependencies Resolved  
> &npsb;  
> ================================================================================  
> Package Arch Version Repository Size  
> ================================================================================  
> Removing:  
> kernel x86\_64 3.10.0-693.el7.centos.tony\_base installed 59 M  
> &npsb;  
> Transaction Summary  
> ================================================================================  
> Remove 1 Package  
> &npsb;  
> Installed size: 59 M  
> Is this ok \[y/N\]: y  
> Downloading packages:  
> Running transaction check  
> Running transaction test  
> Transaction test succeeded  
> Running transaction  
> Erasing : kernel-3.10.0-693.el7.centos.tony\_base.x86\_64 1/1  
> Verifying : kernel-3.10.0-693.el7.centos.tony\_base.x86\_64 1/1  
> &npsb;  
> Removed:  
> kernel.x86\_64 0:3.10.0-693.el7.centos.tony\_base  
> &npsb;  
> Complete!