Posted on Sunday March 13, 2016 by Eric Potvin
pre-installed Ubuntu Server are not configured with SWAP. Linux swaps allow a system to harness more memory than was originally physically available
Check for SWAP space:
Let's check if a SWAP file exists and it's enabled before we create one.
sudo swapon -s
If there's no SWAP file, you should get a result like this:
Filename Type Size Used Priority
Create and Enable the Swap File
Before we create the SWAP file, we need to find out how much we need. Here's a quick guide to help you.
|RAM in your Server||Recommended swap space|
|2GB of RAM or less||2 times the amount of RAM|
|2GB to 8GB of RAM||Equal to the amount of RAM|
|8GB to 64GB of RAM||0.5 times the amount of RAM|
|64GB of RAM or more||4GB of swap space|
To create the SWAP file, you will need to use the
sudo dd if=/dev/zero of=/swapfile bs=1024 count=512k
All of this means:
if=/dev/zero : Read from /dev/zero file. /dev/zero is a special file in that provides as many null characters to build storage file called /swapfile1. of=/swapfile1 : Read from /dev/zero write stoage file to /swapfile1. bs=1024 : Read and write 1024 BYTES bytes at a time. count=524288 : Copy only 523288 BLOCKS input blocks.
Prepare the swap file by creating a linux swap area:
sudo mkswap /swapfile
The results display:
Setting up swapspace version 1, size = 524284 KiB no label, UUID=265d3e61-6e2b-4126-baba-6e6185e97b46
Activate the swap file:
sudo swapon /swapfile
Confirm that the swap partition exists.
$ sudo swapon -s
This will output something like:
Filename Type Size Used Priority /swapfile file 524284 0 -1
This will last until the server reboots. Before, rebooting the server. Let's create the entry in the fstab:
sudo vi /etc/fstab
and add the following line:
/swapfile none swap sw 0 0
Swappiness in the file should be set to 0. Skipping this step may cause both poor performance, whereas setting it to 0 will cause swap to act as an emergency buffer, preventing out-of-memory crashes. You can do this with the following commands:
echo 0 | sudo tee /proc/sys/vm/swappiness echo vm.swappiness = 0 | sudo tee -a /etc/sysctl.conf
To prevent the file from being world-readable, you should set up the correct permissions on the swap file:
sudo chown root:root /swapfile sudo chmod 0600 /swapfile
Reboot to make sure the new swap gets activated properly at startup.