How did I upgrade gymstar.ca from Magento 2.1.9 to 2.2.6?

Step 1

bin/magento maintenance:enable

Step 2

I upgraded third-party packages and ensured that it does not break the website:

composer self-update
composer clear-cache
rm -f composer.lock
composer update --prefer-source
bin/magento setup:upgrade
rm -rf var/generation var/cache var/log var/page_cache var/view_preprocessed
bin/magento setup:di:compile
rm -rf pub/static/* && bin/magento setup:static-content:deploy en_US en_CA
bin/magento indexer:reindex && bin/magento cron:run

Step 3

composer require magento/product-community-edition 2.2.6 --no-update
composer update --prefer-source
rm -rf var/generation var/cache var/log var/page_cache var/view_preprocessed

Step 4

How to fix the «Unable to unserialize value» failure while upgrading Magento from 2.1.x to 2.2.x?

Step 5

How to fix the «Email has a wrong format» failure while upgrading Magento from 2.1.x to 2.2.x?

Step 6

Step 7

UPDATE quote_item_option SET value = 'a:6:{s:4:"uenc";s:76:"aHR0cHM6Ly93d3cuZ3ltc3Rhci5jYS9nYXNwLXRyYWluaW5nLWJlbHQtYmxhY2suaHRtbC5odG1s";s:7:"product";s:2:"94";s:28:"selected_configurable_option";s:2:"12";s:15:"related_product";s:0:"";s:15:"super_attribute";a:1:{i:137;s:3:"160";}s:3:"qty";s:1:"1";}' WHERE option_id = 117439;

Step 8

bin/magento setup:upgrade
rm -rf var/di var/generation generated/code && bin/magento setup:di:compile
rm -rf pub/static/* && bin/magento setup:static-content:deploy -f en_US en_CA &&
bin/magento indexer:reindex && bin/magento cron:run

Step 9

How to fix the «Character content other than whitespace is not allowed» XML DOM error?

Step 10

MageBright «Assign Order to Customer»: How to fix the «Invalid Document» / «Element ‘resource’: The attribute ‘title’ is required but missing» failure in Magento 2.2?

Step 11

How to remove «As low as» after upgrading Magento to 2.2.4?

Step 12

How to fix the «Unexpected token , in JSON» issue with the «showCaption» parameter of a media gallery in a third-party design theme?

Step 13

How to restore the frontend product gallery dimensions in a third-party design theme after upgrading Magento from 2.1.x to 2.2.x?

Step 14

How to fix the «No such entity» error on a product save in Magento 2.2.6?

Step 15

bin/magento maintenance:disable