As your Magento store grows in size with more products, orders and customers, you may experience difficulty while re-indexing data through Magento's web admin interface. Fear not - it is possible, and advisable, to run the reindexing through command line using SSH.

1. Log in to your server or hosting account via SSH, ensuring you use the same credentials as the Magento installation (i.e. never log in with root)
2. Navigate to /public_html/shell/ folder
3. Check the status of the indexes to see what needs reindexing
   php indexer.php --status
4. To reindex all
   php indexer.php --reindexall
5. Or, find the key names of each index and reindex only the items requiring a reindex
   php indexer.php --info
6. Running the above will give you a list as follows:
   catalog_product_attribute
   Product Attributes
   catalog_product_price
   Product Prices
   catalog_url
   Catalog URL Rewrites
   catalog_product_flat
   Product Flat Data
   catalog_category_flat
   Category Flat Data
   catalog_category_product
   Category Products
   catalogsearch_fulltext
   Catalog Search Index
   cataloginventory_stock
   Stock Status
   tag_summary
   Tag Aggregation Data
7. Now choose the key names that require reindexing and run, seperating with a comma if more than one
   php indexer.php --reindex key_name_here
8. As an example, if we need to reindex catalog_product_flat and catalog_category_product we would choose
   php indexer.php --reindex catalog_product_flat,catalog_category_product
9. Now we wait until completion - you'll get a message after it's done telling you how long it took to complete