Publication date: 2020-05-13
When trying to update a website using Sitecopy (a mirroring tool), I unexpectedly got an error "permission denied". A series of troubleshooting steps followed - checking permissions, trying to ftp manually to the site, etc. Finally I realized that everything was working except of creating a directory named "lib".
A directory named "lib" (and similarly "etc") cannot be created via ftp using proFTPD due to a feature that aims at providing some additional protection against a class of attacks. This security feature can be controlled using the "RLimitChroot".
I thus temporarily disabled the "RLimitChroot" protection, mirrored my website, and finally returned to the original configuration.
The proFTPD configuration is described in the manual.