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+grub2-set-default
+===
+
+设置系统默认的启动内核
+
+## 语法
+
+```shell
+Usage: grub2-set-default [OPTION] MENU_ENTRY
+Set the default boot menu entry for GRUB.
+This requires setting GRUB_DEFAULT=saved in /etc/default/grub.
+
+  -h, --help              print this message and exit
+  -v, --version           print the version information and exit
+  --boot-directory=DIR    expect GRUB images under the directory DIR/grub2
+                          instead of the /boot/grub2 directory
+
+MENU_ENTRY is a number, a menu item title or a menu item identifier.
+
+Report bugs to <bug-grub@gnu.org>.
+
+```
+
+## 实例
+
+查看可选的系统内核：
+```shell
+# awk -F\' '$1=="menuentry " {print $2}' /etc/grub2.cfg
+CentOS Linux (5.4.219-1.el7.elrepo.x86_64) 7 (Core)
+CentOS Linux (3.10.0-1160.76.1.el7.x86_64) 7 (Core)
+CentOS Linux (3.10.0-862.el7.x86_64) 7 (Core)
+CentOS Linux (0-rescue-3221d376917c458992a952d6327f2d6a) 7 (Core)
+```
+
+grub2-set-default后面的序号从0开始。所以，如果想设置第一个选项为默认启动内核，则可以使用下面的命令：
+
+```shell
+# grub2-set-default 0
+```
+如果想使用CentOS Linux (3.10.0-862.el7.x86_64) 7 (Core)内核版本,则可以将0改为2
+
+重启系统
+```shell
+~]# init 6
+```
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