Shield Plugin Upgrade & Install Issues

When WordPress installs a plugin, it does the following:

  1. Downloads the ZIP archive files
  2. Stores the ZIP file in a temporary location
  3. Unpacks the ZIP file
  4. Removes existing plugin directory if it's an upgrade
  5. Copy/Move all files from the unpacked ZIP to the plugin directory
  6. Deletes any temporary files.

That's a lot of steps, and responsibility for performing all of these steps correctly is up to WordPress itself, and the web hosting server.

The plugin itself being installed, cannot alter or adjust this process.

If the operate is interrupted at any stage, then your site could be left in a very unpredictable state.

What Could Interrupt The Upgrade/Install Process?

A number of different things could break this process, e.g.:

1) The server that serves the ZIP file could have issues and provide an incomplete ZIP file.

2) Your web hosting server might have limited disk space available and download and/or unpacking the ZIP file may fail as it can't write the new files to disk.

3) Disk permission on the original plugin directory (if it exists) could restrict file deletion or creation of a new plugin folder.

4) If as outlined in scenario (1) an incomplete ZIP file is downloaded, the plugin that is copied to the plugin directory may be incomplete and you're left with essentially an invalid plugin with missing files.

5) Most webhosts have an execution timeout limit, of around 15 seconds. If your webhost is under strain and processing is slowed and the plugin is sufficiently large, copying the files to the new plugin directory could get interrupt part-way through the process leaving you with an incomplete plugin installation (this is quite common!)

What Are The Consequences of an Interrupted Plugin Install?

Depending on where in the process the installation was interrupted, you'll be left with a plugin that is incomplete and is likely to cause fatal errors when WordPress loads.

There is no way to mitigate this problem, except to have a high performing webhost, or one that doesn't have a low execution timeout limit.

What To Do With A Corrupted Plugin Install?

If it's causing fatal errors, WordPress' built-in protection may alleviate this and let you run in a recovery mode.

Failing that, you'll need to access your WordPress file system using a filemanager or FTP.

You'll need to delete the plugin and attempt and reinstallation.

Failing that again, you'll want to use a file manager and manually upload the plugin files to your site.