First check the baseline. It is possible that you have some swap already, like a swap partition (a dedicated disk partition only used for swap) or a swap file, like we are creating in this tutorial.
Use the command: ‘swapon -s‘ In the output there is something like this:
Filename Type Size Used Priority /dev/dm-0 partition 4159484 543024 -1
Another way to check your memory/swap is using the command ‘free‘. Execute the command: ‘free’ to check there is i.e. no swap at all. See field: Swap: X total -> 0
total used free shared buffers cached Mem: 114404 83756 30648 0 2856 23460 -/+ buffers/cache: 57440 56964 Swap: 0 0 0
Remark: The examples to check the baseline are from different systems.
Create swap file
In this example, we will create a swap file of 512 MB.
sudo dd if=/dev/zero of=/tmp/swapfile bs=1M count=512 sudo chmod 600 /tmp/swapfile sudo mkswap /tmp/swapfile
- Create a file of 512 MB, filled with zeros.
- Set the permissions of the file to read-write for root only. Otherwise other users can peek into the data of other users, stored in (cache) memory.
- Create a swap file system on the newly created file.
Now it’s time to tell the system that we have a swap file available:
sudo swapon /tmp/swapfile
Check again using ‘swapon -s’
Filename Type Size Used Priority /dev/dm-0 partition 4159484 542572 -1 /tmp/swapfile file 524284 0 -2
Besides of the original swap partition, we also see a swap file. Mission accomplished!
Using the ‘free’ command (at the other system) we see:
total used free shared buffers cached Mem: 114404 83756 30648 0 2856 23460 -/+ buffers/cache: 57440 56964 Swap: 524284 0 524284
As you can see at field: Swap: X total, there is 524284 bytes swap space allocated.