We recommend the permission setting for the SQLyog tunneller file to be (in octal notation) 644. That means read permission for both 'owner', 'group' and 'all' and write permission for 'owner' (only).
Actually no write permission is required at all, but public read permission most often is, if the webserver shall be able to use the file (unless the user/group structure is much different from the standard setups of most OS's). So also 444 works, but if you use this then you will need to change back in advance should you want to delete or replace it.
However we also have a few reports that settings higher than 644 like 664 (that additionally gives write access to 'group') in rare situations will raise an internal webserver error (reported as HTTP error 500 in a browser). Currently we are not sure about why it happens sometimes. It may be
* An issue with a specific OS
* Some special server directive in action
* Some special way the webserver is installed/configured in the OS
Any additional insight into this will be much appreciated!
Some hosting services (such as Hostgator) use this approach to enforce the use of "secure" file permissions on shared servers - e.g. to prevent someone over-writing your html files and possibly hijacking your site.
Found out the hard way installing ClickCartPro!
Permissions of 755 on html files would throw a 500 internal server error. On checking the server error log I found that the reason for the 500 error was the permissions on some files. Changing to 644 fixed the problem.
Added at: 2008-09-13 18:29