Linux Grub2 Set Default(手動設定開機時要啟動的 linux 核心)

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# 1. 查看目前已經有安哪些核心
grep ^menuentry /boot/grub2/grub.cfg

# 2. 選擇核心
grub2-set-default 0

# 3. 重新生成GRUB配置
grub2-mkconfig -o /boot/grub2/grub.cfg

# 4. 重新開機
reboot

# 5. 檢查
uname -a

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[root@test-os yum.repos.d]# grep ^menuentry /boot/grub2/grub.cfg
menuentry 'Oracle Linux Server 7.9, with Unbreakable Enterprise Kernel 4.14.35-2047.537.4.el7uek.x86_64' --class oracle --class gnu-linux --class gnu --class os --unrestricted $menuentry_id_option 'gnulinux-4.14.35-2047.537.4.el7uek.x86_64-advanced-cf7b3276-fddb-46de-917a-bbb2ca596c54' {
menuentry 'Oracle Linux Server 7.9, with Unbreakable Enterprise Kernel 4.14.35-1902.300.11.el7uek.x86_64' --class oracle --class gnu-linux --class gnu --class os --unrestricted $menuentry_id_option 'gnulinux-4.14.35-1902.300.11.el7uek.x86_64-advanced-cf7b3276-fddb-46de-917a-bbb2ca596c54' {
menuentry 'Oracle Linux Server 7.9, with Linux 3.10.0-1160.119.1.0.1.el7.x86_64' --class oracle --class gnu-linux --class gnu --class os --unrestricted $menuentry_id_option 'gnulinux-3.10.0-1160.119.1.0.1.el7.x86_64-advanced-cf7b3276-fddb-46de-917a-bbb2ca596c54' {
menuentry 'Oracle Linux Server 7.9, with Linux 3.10.0-1127.el7.x86_64' --class oracle --class gnu-linux --class gnu --class os --unrestricted $menuentry_id_option 'gnulinux-3.10.0-1127.el7.x86_64-advanced-cf7b3276-fddb-46de-917a-bbb2ca596c54' {
menuentry 'Oracle Linux Server 7.9, with Linux 0-rescue-3cba3f4f70964a3f99b4af515dd515e1' --class oracle --class gnu-linux --class gnu --class os --unrestricted $menuentry_id_option 'gnulinux-0-rescue-3cba3f4f70964a3f99b4af515dd515e1-advanced-cf7b3276-fddb-46de-917a-bbb2ca596c54' {
[root@test-os yum.repos.d]# grub2-set-default 0
[root@test-os yum.repos.d]# sudo grub2-mkconfig -o /boot/grub2/grub.cfg
Generating grub configuration file ...
Found linux image: /boot/vmlinuz-4.14.35-2047.537.4.el7uek.x86_64
Found initrd image: /boot/initramfs-4.14.35-2047.537.4.el7uek.x86_64.img
Found linux image: /boot/vmlinuz-4.14.35-1902.300.11.el7uek.x86_64
Found initrd image: /boot/initramfs-4.14.35-1902.300.11.el7uek.x86_64.img
Found linux image: /boot/vmlinuz-3.10.0-1160.119.1.0.1.el7.x86_64
Found linux image: /boot/vmlinuz-3.10.0-1127.el7.x86_64
Found initrd image: /boot/initramfs-3.10.0-1127.el7.x86_64.img
Found linux image: /boot/vmlinuz-0-rescue-3cba3f4f70964a3f99b4af515dd515e1
Found initrd image: /boot/initramfs-0-rescue-3cba3f4f70964a3f99b4af515dd515e1.img
done