Can't find it explicitly stated in the docs, but I think this comment's suggestion holds true for Confluence as well as Jira: https://github.com/afklm/jira/issues/37
If you executed the Linux Installer with 'root' user privileges, the Linux Installer creates a dedicated Linux user account with username 'confluence', which is used to run Confluence. This account has only:
Full write access to your Confluence Home and other important directories.
Limited write access to your Confluence Installation Directory.
Can't find it explicitly stated in the docs, but I think this comment's suggestion holds true for Confluence as well as Jira: https://github.com/afklm/jira/issues/37
I found it alluded to in the "Please note" section