安装了win10，然后又安装了manjaro，最后又安装了Ubuntu。开机默认就是进入的Ubuntu的grub，然而我比较喜欢manjaro的grub主题。在bios中设置manjaro的引导为默认引导，但是此时manjaro的grub没有Ubuntu，进入到manjaro系统，执行如下命令即可：
sudo update-grub原文：https://askubuntu.com/questions/649816/add-new-menu-items-to-grub-boot-menu
Grub menu entries are auto-generated by sudo update-grub. Have you tried to run it ? Doesn't it suite your needs ?
Otherwise, you can use /etc/grub.d/40_custom to add your custom entries. And then run sudo update-grub to update /boot/grub/grub.cfg.
You can however edit manually /boot/grub/grub.cfg to delete an entry. But your change will be lost the next time update-grub will be run by you or automatically by ubuntu when there is a kernel upgrade.