在许多ACPI管理的系统里，CentOS 7引导程序Grub2在执行关机"halt"指令时会失败，屏幕显示如下出错信息：
grub> halt Unknown opcode 0x6 Unknown opcode 0x12 Unknown opcode 0x7d ACPI shutdown failed
此时，只能长按电源按钮强行关机。
Grub上游源代码已经整合了一个能解决这个问题的补丁，但仍未被大多数Linux发行版采纳。
我刚把这个补丁（删除了无法正确合并的ChangeLog片段）加入了CentOS 7的Grub2 SRPM软件包；RPM包可从http://dl.zhmail.com/rhel/7/x86_64/目录下载。
CentOS 7中Grub 2升级步骤如下：
$ sudo rpm -Fvh grub*.x86_64.rpm $ sudo grub2-install --force --skip-fs-probe /dev/sda6 Installing for i386-pc platform. grub2-install: warning: File system ‘xfs’ doesn't support embedding. grub2-install: warning: Embedding is not possible. GRUB can only be installed in this setup by using blocklists. However, blocklists are UNRELIABLE and their use is discouraged.. Installation finished. No error reported.
注意：在以上grub2-install命令中，/dev/sda6是我的笔记本电脑上CentOS 7的/boot分区。执行grub2-install时须根据实际情况调整命令参数。
重启系统后，grub就能正确执行halt指令了。
如果你想在grub启动菜单中增加Shutdown和Reboot两个菜单项，可以在/etc/grub.d/40_custom中加入如下两个menuentry:
#!/bin/sh
exec tail -n +3 $0
# This file provides an easy way to add custom menu entries. Simply type the
# menu entries you want to add after this comment. Be careful not to change
# the 'exec tail' line above.
menuentry 'Shutdown' {
echo 'System shutting down...'
halt
}
menuentry 'Reboot' {
echo 'System rebooting...'
reboot
}
然后，键入以下命令重新生成grub.cfg文件：
$ sudo grub2-mkconfig -o /boot/grub2/grub.cfg