Generating class map fails

[gbkra]

Hello,

 

according to the documentation https://devdocs.prestashop-project.org/8/scale/optimizations/#3-composer-autoloading-optimizations

I should generate class map after installing new module. However after running

composer dump-autoload --optimize --no-dev --classmap-authoritative

I do get

Composer could not find a composer.json file in /X/public

To initialize a project, please create a composer.json file. See https://getcomposer.org/basic-usage

Any help on this? Its 1.7.8.8 on nginx. It should be run in specific directory or? THank you in advance.