Yes, I searched the forum quite intensively. But I did not find a thread which answers the question without metnioning cpanel or "ask your provider".
I have a installed oxwall (1.6) on a virtual machine (ubuntu) on my desktop machine (win7). I am also quite experienced in dealing with a naked linux server.
The FTP service on the oxwall server (vsftpd) is up and running. It is configured to accept also local connections (local_enable=YES) and that logged in users have write access (write_enable=YES).
The apache service runs as www-data:www-data user/group. The whole oxwall installation is chown www-data:www-data. I did not change any access rights. During installation oxwall seems to succeed with creating and changing files/directores as needed.
Nevertheless when I enter my credentials into the oxwall update dialog ("Enter attributes") it complains: "Provided user doesn't have permissions to overwrite files."
Looking at the FTP-log file I can watch that a local ftp client (from point of view of the ubuntu server) successfully connects and logs in, then some CWD commands are issued until the current directory is the root of my oxwall install directory (<oxwall>:
Thu Oct 30 21:08:07 2014 [pid 2590] [heri] FTP command: Client "127.0.0.1", "CWD oxwall"
Thu Oct 30 21:08:07 2014 [pid 2590] [heri] FTP response: Client "127.0.0.1", "250 Directory successfully changed."
Thu Oct 30 21:08:07 2014 [pid 2590] [heri] FTP command: Client "127.0.0.1", "CWD"
Thu Oct 30 21:08:07 2014 [pid 2590] [heri] FTP response: Client "127.0.0.1", "550 Failed to change directory."
Thu Oct 30 21:08:07 2014 [pid 2590] [heri] FTP command: Client "127.0.0.1", "MKD var/www/oxwall/ow_core/test"
Thu Oct 30 21:08:07 2014 [pid 2590] [heri] FTP response: Client "127.0.0.1", "550 Create directory operation failed."
Thu Oct 30 21:08:07 2014 [pid 2590] [heri] FAIL MKDIR: Client "127.0.0.1", "/var/www/oxwall/var/www/oxwall/ow_core/test"
Thu Oct 30 21:08:07 2014 [pid 2590] [heri] FTP command: Client "127.0.0.1", "QUIT"
Thu Oct 30 21:08:07 2014 [pid 2590] [heri] FTP response: Client "127.0.0.1", "221 Goodbye."
The first failing command is a CWD without parameters. Then the "MKD var/www/oxwall/ow_core/test" command is very suspicious (when not even wrong: The leading slash is missing). The FTP demon correctly complains that directory "/var/www/oxwall/var/www/oxwall/ow_core/test" cannot be created (ubuntu took the given path as relative to the actual dir). My Oxwall directory has the access rights "drwxr-xr-x 18 www-data www-data" which means that user heri - although member of group www-data - has not write permission to this folder.
Why wants Oxwall create folders through FTP if it could do this also directly? I cannot login as www-data user because this is a system user without login.