How to enable the swap

Hi,

I created a swap partition of 512MB .My machine has 1 GB RAM. The swap entry is present in the /etc/fstab file. But when I give mount command the swap partition is not getting mounted. When I give free command or swapon -s command
Filename Type Size Used Priority
/dev/sda2 partition 522104 0 0

How can I enable the swap ?
Does the swap comes into effect only when the system goes out of memory.

Thanks
Jomy

to enable swap use:

Code:

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swapon /dev/sda2

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though swap should be activated at boot.

Swap is used to store multiples of things usually, e.g. if you have 5 emacs open, their will be multible uses of the memory for the same thing, so lets say four of these processes are put in the swap, while the other that's lot is used for all the sessions of emacs. Though when you fill up your RAM, usually the swap space then gets used for a wider range of things.