电脑双系统centos+windows，安装完centos8之后默认没有引导windows的入口，按照下面方法手搓即可。
1 启动进入centos
查看磁盘分区信息，如下：
fdisk -l
# fdisk -l
Disk /dev/sda: 238.5 GiB, 256060514304 bytes, 500118192 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x297f5cef
Device Boot Start End Sectors Size Id Type
/dev/sda1 * 2048 250058751 250056704 119.2G 7 HPFS/NTFS/exFAT
/dev/sda2 250058752 393418751 143360000 68.4G 7 HPFS/NTFS/exFAT
/dev/sda3 393418752 394442751 1024000 500M 83 Linux
/dev/sda4 394442752 500117503 105674752 50.4G 5 Extended
/dev/sda5 394444800 500117503 105672704 50.4G 83 Linux
通过fdisk结果看到windows第一个partion在sda1，对应grub的磁盘索引编号是hd0,1,接下来编辑grub配置文件，自定义配置路径：
vi /etc/grub.d/40_custom
配置示例如下：
#!/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 "Windows" {
set root=(hd0,1)
chainloader +1
}
保存并执行以下命令使自定义配置生效：
grub2-mkconfig --output=/boot/grub2/grub.cfg
OVER.