After creating a CentOS 7 VM, running "yum update" and rebooting causes the VM to fail to boot. The log shows:
"Fatal: VM was not running 1 minute after being started"
All OnApp Versions
CentOS 7 VMs built from OnApp template (possibly any VM upgraded / installed to CentOS 7)
In /boot/grub/grub.conf, there is a missing line for the default kernel. The first entry should look similar to the older entry, the missing line is something like initrd /boot/initramfs-<kernel release>.img
Example lines from /etc/grub.conf:
title CentOS Linux (3.10.0-229.1.2.el7.x86_64) 7 (Core) root (hd0,0) kernel /boot/vmlinuz-3.10.0-229.1.2.el7.x86_64 root=/dev/xvda1 console=tty0 ro vconsole.keymap=us vconsole.font=latarcyrheb-sun16 LANG=en_US.UTF-8 initrd /boot/initramfs-3.10.0-229.1.2.el7.x86_64.img
The simplest way to fix this is from the recovery mode. Mount the failed VM disk and edit file using vi or other text editor.
CentOS 7 template has a custom kernel from OnApp that has missing features to make the VNC console work. The default updated kernel installed with yum update is not guaranteed to work with the console and would leave the VNC console blank / black.