Increase PHP memory limit (3 methods)
While Drupal core will run with 8 MB of memory configured for your server, you may need to increase this depending on how may modules you use on your site.
In Drupal 4.7.x and earlier, when you go into ?q=admin/modules, you may experience a blank screen. This is caused by Drupal loading all the modules of your site into memory, whether you have them turned on or not. If you get a blank screen here, you have two choices; increase your allocated memory for PHP or delete unused modules.
In Drupal 5.x and above, this problem has been fixed, and the modules page no longer loads all modules. If you are still getting out of memory problems, you should either reduce the number of modules used or increase your allocated memory for PHP.
Depending on your host, this can be done in a number of places with the most likely being php.ini or .htaccess depending on your hosting situation.
Add for example:
memory_limit = 16Mto your php.ini file (recommended, if you have access)ini_set('memory_limit', '16M');to your sites/default/settings.php filephp_value memory_limit 16Mto your .htaccess file in the Drupal root
With root access, you can use the sed util in Linux/Unix based systems, in order to increace the memory for 64M. Don't forget to properly locate you php.ini file!
sed -i 's/memory_limit = 16M/memory_limit = 64M/' /etc/php5/apache2/php.iniYou will need to experiment with the value that is right for you depending on which modules you are using. Some people find they need to set the memory to 24M or 32MB or higher (e.g. 96MB is recommended for a site with built-in image processing using ImageAPI GD).
NOTE: Some hosts do not allow you to control how much PHP memory is available. In this case you will need to work with your host, be very conservative with your module selection and testing or look for a new host that allows more flexibility.

If you're going to have views
If you're going to have views or any kind of image processing, don't be shy, set to at least 128M!
I recommend 512M, if you can get away with it.
change permissions to edit settings.php
A tip for editing settings.php: I tried to edit
settings.phpand got errors, so I tried uploading an edited version... and got errors. The I remembered that the permissions are set to555, which means "no one can edit this file", so I changed permissions to775, added the recommended line and saved, then changed permissions back to555, and it worked! Note: I did this one a brand new site with no users besides me. It's probably dangerous to editsettings.phpon a live site with other users.On some shared hosts (I use
On some shared hosts (I use Hostpapa) they allow you to change this by uploading a php.ini file to the root of your domain. This allows you full control of your php settings.