From here
http://help.joomla.org/content/view/40/168/File System Permissions
On POSIX based systems (like Unix, Linux, etc), you will need to change the permissions. There are two methods to do this, of which the first is recommended:
Telnet, or secure shell, to your server. Enter the following system command:
> ps -ef | grep apache
You may have to change the name of the process, depending on your system (for example, the process name could be httpd). You may receive output like the following:
root
7508 1 0 08:
58 ?
00:
00:
00 /usr/local/apache/bin/httpd nobody
7511 7508 0 08:
58 ?
00:
00:
00 /usr/local/apache/bin/httpd nobody
7512 7508 0 08:
58 ?
00:
00:
00 /usr/local/apache/bin/httpd nobody
7513 7508 0 08:
58 ?
00:
00:
00 /usr/local/apache/bin/httpd nobody
7514 7508 0 08:
58 ?
00:
00:
00 /usr/local/apache/bin/httpd nobody
7515 7508 0 08:
58 ?
00:
00:
00 /usr/local/apache/bin/httpd nobody
7521 7508 0 08:
58 ?
00:
00:
00 /usr/local/apache/bin/httpd nobody
7522 7508 0 08:
58 ?
00:
00:
00 /usr/local/apache/bin/httpd nobody
7523 7508 0 08:
58 ?
00:
00:
00 /usr/local/apache/bin/httpd
This tells you that the user "nobody" is running the web server process. Change to the Joomla directory. Enter the following system command (substitute the user name appropriate for your system):
> chown -R nobody .
WARNING: Make sure the user you use to ftp or Administer the site is in the file system group, and that all files have the permission set to 775. If you don't you may not be able to edit files on the file system remotely.
- The second method, is to change the permissions of the images/, media/,uploadfiles/ and administrator/backups directories to 707, this should be done recursively:
chmod -R 707 images chmod -R 707 media chmod -R 707 uploadfiles chmod -R 707 components chmod -R 707 languages chmod -R 707 modules chmod -R 707 templates chmod -R 707 administrator/backups chmod -R 707 administrator/components chmod 744 configuration.php
--Slixter