chmod command (abbreviated from change mode) is a Unix command that lets a programmer tell the system how much (or little) access it should permit to a mediawiki file.
Accessing files 
If you are using FTP software, there is usually a menu option or button that says "Change Permissions," click this option. You have choices of R(read), W(write), and X(execute).
If you are using a program such as PuTTy, you need to use the "chmod" command.
|Read permissions||chmod 744 yourfile|
|Execute permissions||chmod 755 yourfile|
|Read/write permissions||chmod 766 yourfile|
|All permissions||chmod 777 yourfile|
- Tutorial for chmod
- If you are changing permissions for scripts in Perl/CGI, you need to make sure they have execute permissions.
- How can I change permissions on my files?
See also 
- chmod wikipedia