My OJS site have hard links in their path. What does it mean?

Hello,

I installed the latest version of OJS on my server for testing before updating my official site and when the server is backed up, the system cannot back up the account content due to the presence of hard links:

User xxxxx has one or more hard links in their path:
/home/xxxxx/domains/xxxxx.com/public_html/ojs/lib/pkp/lib/vendor/bin/carbon
/home/xxxxx/domains/xxxxx.com/public_html/ojs/lib/pkp/lib/vendor/bin/export-plural-rules
/home/xxxxx/domains/xxxxx.com/public_html/ojs/lib/pkp/lib/vendor/bin/lessc
/home/xxxxx/domains/xxxxx.com/public_html/ojs/lib/pkp/lib/vendor/gettext/languages/bin/export-plural-rules
/home/xxxxx/domains/xxxxx.com/public_html/ojs/lib/pkp/lib/vendor/nesbot/carbon/bin/carbon
/home/xxxxx/domains/xxxxx.com/public_html/ojs/lib/pkp/lib/vendor/wikimedia/less.php/bin/lessc

I am using CentOS and DirectAdmin

thanks!