Swap

Memory is finite and can run out. In some cases, it would be best to fail and emit an OOM error to users. Alternatively, swap space can be used to keep a process running without failure visible to users.

Swap is inherently slower than memory. Furthermore the process of writing memory pages into swap (and eventually loading them back from swap) can make I/O a significant bottleneck. For these reasons and more, swap does carry a cost.

Setup

Create a new swap file.

# for 2GB
sudo dd if=/dev/zero of=/swap bs=1024 count=2097152
sudo chmod 600 /swap
sudo mkswap /swap

Add the file as swap.

sudo swapon /swap

To verify that the file is being used as swap, try:

swapon -s

And to make the swap persistent, add the following to fstab(5):

/swap    swap    swap   defaults 0 0

Administration

Enable or Disable

To temporarily enable or disable swap, try:

sudo swapon /swap
sudo swapoff /swap

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