Modules are prioritized and called in the inverse order of which they were loaded. In other words, the last loaded module is the first to receive calls for a particular configuration directive, FTP command or authentication request.
This can be used to allow later loaded modules (higher priority) to possibly "override" early loaded (lower priority) modules. The load order of modules is thus very important.
To see just what your module load order is, use:
$ proftpd -l
Compiled-in modules:
mod_core.c
mod_xfer.c
mod_rlimit.c
mod_auth_unix.c
mod_auth_file.c
mod_auth.c
mod_ls.c
mod_log.c
mod_site.c
mod_delay.c
mod_facts.c
mod_auth_pam.c
mod_tls.c
The modules will be listed from lowest priority to highest priority.
Note, however, if that you use DSO/shared modules, then the module load order
is determined by the order of the
LoadModule
directives in your configuration. Again, the last module loaded via
LoadModule will be the first module called.