How to fix the «cache_dir "var/cache" is not writable» issue?

dmitrii_fediuk (Dmitrii Fediuk) July 11, 2017, 10:36am 2

See also:

How to fix the «Can’t create directory ‘generated/code’ in Magento/Framework/Code/Generator.php» Magento 2.2 issue?
How to fix the «Can’t create directory var/generation» issue?