1. __kernel_update() {
    2.     #导入公钥
    3.     rpm --import https://www.elrepo.org/RPM-GPG-KEY-elrepo.org
    4.     #添加YUM源
    5.     yum install -y https://www.elrepo.org/elrepo-release-7.el7.elrepo.noarch.rpm
    6.     #安装更新长期支持版内核
    7.     yum install -y --enablerepo=elrepo-kernel kernel-lt kernel-lt-devel
    8.     #更新GRUB配置使用新内核启动
    9.     #查看配置中的所有内核版本
    10.     awk -F\' '$1=="menuentry " {print i++ " : " $2}' /etc/grub2.cfg
    11.     _modify=$(awk -F\' '$1=="menuentry " {print i++ " : " $2}' /etc/grub2.cfg | head -1 | grep "$(uname -r)" -c)
    12.     if ((_modify != 1)); then
    13.         #设置新内核为默认启动项,默认情况下新内核序号为0
    14.         grub2-set-default 0
    15.         #更新配置
    16.         grub2-mkconfig -o /boot/grub2/grub.cfg
    17.         # 设置开机免输入密码
    18.         sed -i 's,^ExecStart=.*$,ExecStart=-/sbin/agetty --autologin root --noclear %I,' /etc/systemd/system/getty.target.wants/getty@tty1.service
    19.         sed -i 's,^ExecStart=.*$,ExecStart=-/sbin/agetty --autologin root --noclear %I,' /lib/systemd/system/autovt@.service
    20.         # 修改系统启动等待时间
    21.         sed -i 's,timeout=5$,timeout=2,' /boot/grub2/grub.cfg
    22.         sed -i 's,timeout=5$,timeout=2,' /boot/efi/EFI/centos/grub.cfg
    23.         sync
    24.         # reboot
    25.     fi
    26. }
    27. __kernel_update

    参考文档
    http://blog.itpub.net/6906/viewspace-2657192/
    https://www.jianshu.com/p/e20863f365c4
    https://blog.csdn.net/zxloveooo/article/details/104921010