If you have multiple operating systems installed on your server, you need to select which one you want from the boot loader menu.
如果服务器中安装了多个操作系统，您需要从引导加载程序菜单中选择需要引导的操作系统。
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One of the most straightforward ways is to create dual-boot setups, where multiple OSes are installed on a single machine, with a choice being made at startup as to which one to load.