PHP: Add an Extension

The following relates to the GD Graphics Extension but I think the process is similar for most extensions.

The output of phpinfo() may indicate whether an extension is enabled. If GD is enabled there will be a section for it showing configuration for it. Also, of course, it should be possible to use the extension (for example functions provided by the extension).

Also looking at phpinfo() will give the name and path of the main configuration file. I found that this was /etc/php/8.1/apache2/php.ini. It also gives the name and path of a directory to scan for additional .ini files. In my case it is /etc/php/8.1/apache2/conf.d/. The conf.d directory has a lot of file links to files in a mods-available directory. For example:

an entry in conf.d

lrwxrwxrwx 1 root root   34 Dec  7 00:19 20-gd.ini -> /etc/php/8.1/mods-available/gd.ini

Much of the above information is not necessary for installing a new extension which, at least in some cases, is very simple. The answer to my Stack Overflow question is probably sufficient:

You can run php -v to see what version of PHP you have on the machine. After that, you can run sudo apt-get install php<your-php-version>-gd, e.g. sudo apt-get install php8.1-gd. Hope it helps!

Configuration seems to be handled automatically as there was no need for me to change anything. Doing the above worked. I do not know if it started and stopped Apache but I did not have to do that. I assume that the file link in conf.d and the file it links to in mods-available were generated automatically.