CentOS 7
- 查看系统内部有多少个内核：
cat /boot/grub2/grub.cfg |grep menuentry
- 配置从默认内核启动，下面命令的内核名称根据系统内部查到的实际名称来替换：
grub2-set-default “CentOS Linux (4.4.138) 7 (Core)”
- 验证是否配置成功：
grub2-editenv list
Ubuntu16.04
- 0.环境准备
Ubuntu16.04，内核版本4.10.0，新内核版本4.4.137 - 1.修改grub配置文件
编辑/etc/default/grub文件，将其中的GRUB_DEFAULT的值修改为saved
sudo gedit /etc/default/grub
- 2.查看系统内部已安装的内核
sudo cat /boot/grub/grub.cfg | grep menuentry
选择新的默认内核，内核名称在menuentry后的双引号内，例如上述命令显示结果如下，从其中选择Ubuntu, with Linux 4.4.137作为新的启动内核
menuentry 'Ubuntu, with Linux 4.10.0-28-generic' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-4.10.0-28-generic-advanced-a58882f8-c86d-4817-8517-0b846a106892' {
menuentry 'Ubuntu, with Linux 4.10.0-28-generic (upstart)' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-4.10.0-28-generic-init-upstart-a58882f8-c86d-4817-8517-0b846a106892' {
menuentry 'Ubuntu, with Linux 4.10.0-28-generic (recovery mode)' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-4.10.0-28-generic-recovery-a58882f8-c86d-4817-8517-0b846a106892' {
menuentry 'Ubuntu, with Linux 4.4.137' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-4.4.137-advanced-a58882f8-c86d-4817-8517-0b846a106892' {
menuentry 'Ubuntu, with Linux 4.4.137 (upstart)' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-4.4.137-init-upstart-a58882f8-c86d-4817-8517-0b846a106892' {
menuentry 'Ubuntu, with Linux 4.4.137 (recovery mode)' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-4.4.137-recovery-a58882f8-c86d-4817-8517-0b846a106892' {
menuentry 'Ubuntu, with Linux 4.4.137.old' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-4.4.137.old-advanced-a58882f8-c86d-4817-8517-0b846a106892' {
menuentry 'Ubuntu, with Linux 4.4.137.old (upstart)' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-4.4.137.old-init-upstart-a58882f8-c86d-4817-8517-0b846a106892' {
menuentry 'Ubuntu, with Linux 4.4.137.old (recovery mode)' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-4.4.137.old-recovery-a58882f8-c86d-4817-8517-0b846a106892'
- 2.配置从默认内核启动
sudo grub-set-default xxx
其中xxx为选定的新内核的名称，例如此处的具体命令为
sudo grub-set-default "Ubuntu, with Linux 4.4.137"
更新grub配置
sudo update-grub
但Ubuntu16.04此处会报warning,warning信息如下
Warning: Please don't use old title `Ubuntu, with Linux 4.4.137' for GRUB_DEFAULT, use `Advanced options for Ubuntu>Ubuntu, with Linux 4.4.137' (for versions before 2.00) or `gnulinux-advanced-a58882f8-c86d-4817-8517-0b846a106892>gnulinux-4.4.137-advanced-a58882f8-c86d-4817-8517-0b846a106892' (for 2.00 or later)
warning中推荐使用Advanced options for Ubuntu>Ubuntu, with Linux 4.4.137，因此使用推荐的启动项（双引号内的内容）修改默认启动内核，例如
sudo grub-set-default "Advanced options for Ubuntu>Ubuntu, with Linux 4.4.137"
PS.在本人的测试中发下如果不使用Advanced选项，重启后仍为旧内核；每次grub-set-default后都需要update-grub
- 3.重启验证
sudo reboot
uname -r
