Magento 2.0.18 is the final 2.0.x release. After March 2018, Magento 2.0.x will no longer receive security patches, quality fixes, or documentation updates.
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Update the updater application

In some cases, you might need to update the updater application, which is responsible for updating components and the Magento application. You should do this only if instructed to do so.

To update the updater application:

  1. Log in to your Magento server as, or switch to, the Magento file system owner.
  2. Delete, move, or rename the directory containing the updater application.

    For example,

    mv <your Magento install dir>/update <your Magento install dir>/old_update
  3. Change to your Magento 2 installation directory and enter the following command:

    composer create-project magento/updater update --repository
  4. If prompted, enter your Magento authentication keys.
  5. Wait while Composer installs the updater and its dependencies.