vsftpd上传文件权限配置规则

折腾了老半天才搞清楚规则。在vsftpd.conf内，主要两个配置项相关，运行man vsftpd.conf可以看到：
file_open_mode
              The permissions with which uploaded files  are  created.  Umasks
              are applied on top of this value. You may wish to change to 0777
              if you want uploaded files to be executable.

              Default: 0666

local_umask
              The  value  that the umask for file creation is set to for local
              users. NOTE! If you want to specify octal values,  remember  the
              "0"  prefix  otherwise  the  value  will be treated as a base 10
              integer!

              Default: 077
我需要上传后的文件权限为755，则应该这么配置：
file_open_mode=0755
local_unmask=022 （这个配置表示从file_open_mode赋予的权限中去掉22，即owner group和others的写权限）