Magento 2 Theme Installation Guide

When adding a theme into a Magento 2 install, you don't have run any command line to see if the theme is being seen by Magento. If the code is added to the correct path app/design/frontend/{{vender_namespace}}/{{theme_name}} then the registration.php file will automatically be seen and show up in the admin as a theme to select.

You should be able to navigate to the theme selection in the admin store-> settings-> config-> general-> design-> design theme

If you don't see your theme there, it's installed in the wrong location in the file structure or the registration.php is not correct.

Once you set the theme in the admin, then run the php bin/magento setup:static-content:deploy command from the root of your Magento install and the files will compile into the pub/static folder.

Running the php bin/magento setup:upgrade command is only needed when installing extensions, which the theme might have packaged in some way. But I have found that most theme developers are still finding out how to package themes, with no clear pattern as of yet. And the only time you need to run the php bin/magento setup:di:compile is when you are getting ready to shift from developer mode to production. The message in the command line that tells you to run that seems to be a hold over from the beta days that never got removed. While developing, I have never needed to use it.

Here is a clarification between the three different modes (source: Magento U Fundamentals course). In bold, the specific points related to your question.

Developer mode

• Static file materialization is not enabled.
• Uncaught exceptions displayed in the browser
• Exceptions thrown in error handler, not logged
• System logging in var/report, highly detailed.

You should use the Developer mode while you are developing customizations or extensions. The main benefit to this mode is that error messages are visible to you. It should not be used in production because of its impact on performance. In Developer mode, static view files are generated every time they are requested. They are written to the pub/static directory, but this cache is not used. This has big performance impact, but any changes a developer makes to view files are immediately visible.

Uncaught exceptions are displayed in the browser, rather than being logged. An exception is thrown whenever an event subscriber cannot be invoked.

System logging in var/report is highly detailed in this mode.

Production mode

• Deployment phase on the production system; highest performance
• Exceptions are not displayed to the user -- written to logs only.
• This mode disables static file materialization.
• The Magento docroot can have read-only permissions.

You should run Magento in Production mode once it is deployed to a production server.

Production mode provides the highest performance in Magento 2.

The most important aspect of this mode is that errors are logged to the file system and are never displayed to the user. In this mode, static view files are not created on the fly when they are requested; instead, they have to be deployed to the pub/static directory using the command-line tool. The generated pages will contain direct links to the deployed page resources.

Any changes to view files require running the deploy tool again.

Because the view files are deployed using the CLI tool, the web user does to need to have write access. The Magento pub/static directory can have read-only permissions, which is a more secure setup on a publicly accessible server.

Default mode

• Used when no other mode is specified
• Hides exceptions from the user and writes them to log files
• Static file materialization is enabled.
• Not recommended / not optimized for production: caching impacts performance negatively.

As its name implies, Default mode is how the Magento software operates if not other mode is specified.

In this mode, errros are logged to files in var/reports and are never shown to a user. Static view files are materialized on the fly and then cached.

In contrast to the developer mode, view file changes are not visible until the generated static view files are cleared.

Default mode is not optimized for a production environment, primarily because of the adverse performance impact of static files being materialized on the fly rather than generating and deploying them beforehand.

In other words, creating static files on the fly and caching them has a greater performance impact than generating them using the static file creation command line tool.