rajoute ça dans ton fichier proftpd.conf:
LogFormat fmtaccess "%t %A %h %a %l %m %r"
ExtendedLog /var/log/proftpd-access.log WRITE,READ fmtaccess
ExtendedLog /var/log/proftpd-auth.log AUTH fmtaccess
ExtendedLog /var/log/proftpd-all.log ALL fmtaccess
ExtendedLog /var/log/proftpd-info.log INFO fmtaccess
ExtendedLog /var/log/proftpd-dirs.log DIRS fmtaccess
ExtendedLog /var/log/proftpd-misc.log MISC fmtaccess