My Linode VPS is still of Ubuntu 16.04 LTS. Seems too old. And the CPU usage is always around 70%.

First, I found that the ghost used most of the CPU. Then I stopped and uninstalled the instance. the CPU usage dropped to about 1%. What are ghost doing there?

Second, I found an article on Linode How to Upgrade to Ubuntu 18.04 LTS . It is easy to follow. Just answer a few questions during installation, then everything is done. But after reboot, I found that the "apt update" always failed. It could reach the server. Then I tried "ping google.com", and just got "temporary failure in name resolution". I solved it finally by following instructions in page How to resolve "Temporary failure in name resolution" issue.

Last, I found that my php-fpm was not started. I solved this by re-install it. Then I found the imagemagick.so load failed. A shared library "libwebp.so.5" could not be found. I find the that there are "libwebp.so" and "libwebp.so.6" somewhere. Both of them point to another shared library. I created one symbol link, and restart the php-fpm. Then the issue is gone.

The services on my VPS are very limited. Only LNMP, and a blog run on Wordpress. The whole update cost me about an hour. Not so bad.