Blog Ghost error Validating Config

After an OS restart I had problems with starting Blog Ghost. The error is:

ghost restart
Ghost instance is not running! Starting...
ℹ Ensuring user is not logged in as ghost user [skipped]
ℹ Checking if logged in user is directory owner [skipped]
✔ Checking current folder permissions
✖ Validating config
✔ Checking content folder ownership
One or more errors occurred.

1) Validating config

Error detected in the production configuration.

The first thing that I do was to run analyze of my ghost installation by:

ghost doctor

Then I saw that the problem is related to my JSON config file:

Error detected in the production configuration.

Message: Config file is not valid JSON

Debug Information:
    OS: Ubuntu, v16.04
    Node Version: v8.11.3
    Ghost-CLI Version: 1.7.1
    Environment: production
    Command: 'ghost restart'

Which was given the first time with ghost restart command.

So I'll check my config file and I remembered that recently I did modifications for changing my mail address. Then I check my JSON file if the format is OK with Siblime Text Editor and Pretty JSON plugin. More info here:

Sublime 4 Reindent JSON File

The new mail section was in red. The problem was that all attributes were without quotes. So after adding the missing quotes and valiting the file again I was able to start my Ghost Blog again.

You can refer to this article in order to add new mail address for ghost blog:

How to configure mail for Ghost Blog