Boot

• Grub 2 - Setting default entry

  Open /etc/default/grub and ensure this line exists:
  GRUB_DEFAULT=saved
   
  Apply the change to grub.cfg by running:
  # grub2-mkconfig -o /boot/grub2/grub.cfg
   
  Now list all possible menu entries
  # grep ^menuentry /boot/grub2/grub.cfg | cut -d "'" -f2
   
  Now set the desired default menu entry
  # grub2-set-default <menu entry title>
   
  Verify the default menu entry
  # grub2-editenv list

grubby

# grubby --default-kernel
# grubby --set-default=/boot/vmlinuz-3.10.0-514.el7.x86_64 

• Enable rc-local in OL7

  cat >> /usr/lib/systemd/system/rc-local.service <<EOF
   
  [Install]
  WantedBy=multi-user.target
  EOF
  chmod +x /etc/rc.d/rc.local
  systemctl enable rc-local.service
  systemctl start rc-local.service
  systemctl status rc-local.service
   
  echo "systemctl restart network.service" >> /etc/rc.d/rc.local

# extract initramfs in RHEL7/Centos7
/usr/lib/dracut/skipcpio initramfs-3.10.0-229.el7.x86_64.img | zcat | cpio -idv

kernel cmd line: debug initcall_debug systemd.log_target=console systemd.journald.forward_to_console=1
serial console in grub:
serial --unit=0 --speed=115200
terminal --timeout=10 console serial
kernel cmd line: console=tty1 console=ttyS0,115200n8