For safety reasons it is not possible to use the exec() command. Unfortunately, this command grants so much access that we can no longer guarantee a stable, safe and fast server environment if we allow its use.
Additionally, exec() would enable you to directly influence the quality of our services for other customers. We obviously want to keep this from happening.
Luckily, there are many alternatives to using exec(). Send us a ticket with your question / reason for wanting to use exec(), and we will gladly help you with a different solution.
(Ewww) Image Optimizer
A question that comes up a lot is whether exec can be used in conjunction with an image optimizer.
In these cases we recommend a cloud plugin, since they do not use server resources. That way the processing of images will not slow down the rest of the site.
A couple of available plugins include Smushit en Ewww.
Smushit is free to use, but that also means the optimization server is quite slow. Additionally, Smushit does not support sites with SSL (https).
Ewww Image Optimizer Cloud is cheap (1 dollar/month), and is problem-free as far as we are concerned. Therefore, we recommend Ewww for these use cases.