Magento fix 500

sudo find app/code lib var pub/static pub/media vendor app/etc \( -type d -or -type f \) -exec sudo chmod g+w {} \; && sudo chmod o+rwx app/etc/env.php
sudo chmod -R 777 /var/www/html

1.product image place holder

Replicate: Stores>Configuration>Catalog>Catalog>Product Image Placeholders>base
Something went wrong while saving this configuration: Can't create directory /var/www/magento.abmgood.com/var/generation/Magento/Cron/Model/Config/Backend/Product/Alert/.

Method :

chmod -R 777 /var/www/html/magento2/var/generation/Magento/Cron/Model

2.Fix There are no commands defined in the “cache” namespace.2.Fix There are no commands defined in the “cache” namespace.

[InvalidArgumentException]
There are no commands defined in the "cache" namespace.

Method :

sudo chmod -R 777 var pub

3. Permission Problem when run “bin/magento setup:upgrade”

sudo chmod -R 777 var/generation/ var/view_preprocessed/ var/cache/ pub/static/

4.magento Deployment config file config.php is not writable.

sudo chmod -R 777 app/etc/