The stream could not be opened in append mode: Failed to open stream: Permission denied code example

Example 1: could not be opened in append mode: failed to open stream: Permission denied

chmod -R 775 storage
chmod -R 775 bootstrap/cache

Example 2: could not be opened in append mode: failed to open stream: Permission denied

sudo chown -R $USER:www-data storage
sudo chown -R $USER:www-data bootstrap/cache