In the /conf folder there is a file called _maintenance.html.

Manually enabling maintenance mode

If you rename this file to maintenance.html (no _ at the beginning), it will put your b2evolution website into maintenance mode, serving a 503 "Not Available" response to any user trying to access your site.

You can modify the contents on the maintenance.html to customize the page your users will see during maintenance.

Accessing the installer during maintenance

You can also rename the file to imaintenance.html (i at the beginning). In that case, your site will still be under maintenance but it will be possible for you to access the /install folder. The /install is the only folder that will no return a 503 page.

This will allow you to perform a DB upgrade without people accessing your site until you are finished.

Automatic Upgrade

The Auto Upgrade Procedure feature will create a similar file called umaintenance.html (u at the beginning). When this file is present, the installer cannot be accessed manually. However the automatic upgrade feature can still work to upgrade your system.

Getting out of maintenance mode

When you are finished with your maintenance, don’t forget to rename the file back to _maintenance.html.