What causes an R script to get Killed?

I've been running some memory intensive processes on EC2 servers. The code runs quite well for about 12-14 hours (it's r开发者_如何学Cunning 1000s of simulations on 12-14 large datasets) and then all of a sudden I just see the message "Killed" with no further explanation.

What makes R do that?

UPDATE: My server specs.

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It could be the out of memory killer of the operating system.

Are you cleaning up your workspace when you have finished with a dataset?

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From what I know, I don't think R has a "killed" error. Most likely it's your operating system imposing a process limit or some kind of quotas. If you are working on a network system, maybe ask your sysadmin?