Because I just posted this description in the post I wrote on how to make WordPress Auto-Thumbnails work, I thought I would also post those instructions straight up as a pointer for anyone out there who is looking for the command required to install the GD Library in their LAMP setup, so here it is:
How to Install GD Library on your LAMP Server
On a centos system, the following command in your SSH terminal will install the GD Library:
yum install php-gd
After you’ve hit “y” and the installation has completed, because this is used by PHP scripts, and is therefore loaded when Apache starts, you’ll also need to restart your apache web server using the following command:
service httpd restart
The above should work on most versions of Centos Linux. You may need to do type “sudo -i” and hit return before doing the above, depending upon your permissions and setup.