For windows and ubuntu systems, the system and wait time settings are selected by default.

In windows and ubuntu systems, grub is enabled after the BIOS of the computer is started based on the system and wait time settings by default, when gurb is started, it will go to www.2cto.com/boot/grub. if you want to modify the default system and wait time, you can modify the content in the/etc/default/grub file. The corresponding commands are as follows: www.2cto.com sudo gedit/etc/default/grubsudo update-grub use the root user to edit the grub file, GRUB_DEFAULT = 0 # GRUB_HIDDEN_TIMEOUT = 0GRUB_HIDDEN_TIMEOUT_QUIET = trueGRUB_TIMEOUT = 10GRUB_DISTRIBUTOR = 'lsb _ release-i-s2>/dev/null | echoDebian 'gr UB_CMDLINE_LINUX_DEFAULT = "quietsplash" GRUB_CMDLINE_LINUX = "" Save and update the grub file to complete the modification. In addition, there is a better way to modify the default priority boot System Option: Check/boot/grub. conf file, find the following content ### BEGIN/etc/grub. d/30_os-prober ### menuentry "Microsoft Windows XP Professional (on/dev/sda1)" {insmod ntfsset root = (hd0, 1) search -- no-floppy -- fs-uuid -- set 4c844b34844b2036drivemap-s (hd0) $ {root} chainloader + 1 }## END/etc/grub. d/30_os-prober ####### some descriptions/etc/grub. the d/30_os-prober file is responsible for adding other system boot items. if you add the startup items added to the file to the first place, the default boot items will be added. We enter/etc/grub. d/directory. the following file is found: 00_header 10_linux 30_oss-prober README 05_debian_theme 20_memtest86 + 40_custom. All files start with numbers and are executed in ascending order. Change the number before 30_os-prober to 09, which is smaller than 10_linux OS. Just execute it a little earlier. For example, 09_os-prober and update the grub configuration file. The command is as follows: sudo cd/etc/grub. d/sudo mv 30_os-prober 09_os-probersudo update-grub