Can I add memory to the Linux box without rebooting the system?

I think Linux check the hardware at booting time. But if I need to add more memory to the server while I do not want to stop the service. Is there some method to make Linux use the new added memories?

The question is not trivial.

The Linux kernel has support for memory hotplug, if that's what you are asking. The second question is whether your hardware supports it or not, though. And Linux can't do anything about that, you should be able to find that on the technical manuals for your hardware. Another question is whether the concrete software you are using will handle it nicely or not. You might need to restart a given program or service so it becomes aware (you will save a reboot at least).

Another question is whether your OS will be able to handle all the RAM. In other words: is it using regular x86, x86 with PAE, x64 or any other architecture? You only need to worry about this if you have less than 4gb or ram and you plan to end up with more than 4gb or ram.

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The old fashioned hardware guy in me shrieks in horror.
Adding ram like plugging in a card would comprehensively blow most systems. Make sure yours is physically hot pluggable. Be aware that kernel support for hot plugging really means the kernel can switch it off.

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Be sure it supports hot add not just hot swap.

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What I want to know is "Linux kernel's support for memory hotplug". I know there are a lot of concerns before doing it.

Thanks a lot for all of you giving kind suggestions!

Such support exists, as said above.

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