How Would I Restrict a Linux Binary to a Limited Amount of RAM?

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http://serverfault.com – I would like to be able to limit an installed binary to only be able to use up to a certain amount of RAM. I don't want it to get killed if it exceeds it, only that that would be the max amount that it could use. The problem I am facing is that I am running an Apache 2.2 server with PHP and some custom code that a developer is writing for us. The problem is that somewhere in there code they launch a PHP exec call that launches ImageMagick's 'convert' to create a resized image file. I'm not privy to a lot of details to the project or the code, but need to find a solution to keep them from k (HowTos)