[Linux] Setting SWAP Space under Linux

Introduction

Swap space is to substitute disk space for RAM memory when RAM fills up. When the RAM is insufficient, idle pages are moved from the RAM to the swap space . The virtual memory contains physical memory and swap.

Approach 1：Create a Swapfile

Using this Approach can increase the swap space in a flexible way, and it can be easily removed when it is not needed. It is suitable for temporary needs or a situation increasing the swap space without stopping the server.

free -m

             total        used        free      shared  buff/cache  available
Mem:           7972        4822        160        487        2989        3175
Swap:           0            0           0

• Create a swapfile
  Navigate to target directory(ex./mnt/resource) to create swapfile：
  

sudo dd if=/dev/zero of=/swapfile bs=1G count=5

The primary purpose of dd(data duplicator) command is to convert and copy files.
if=<filename>：input file name
of=<filename>：output file name
bs=<bytes>：Read and write BYTES bytes at a time
count=<N>：Copy only BLOCKS input blocks

• Change directory permissions

sudo chmod 600 /swapfile

• Create swap space

sudo mkswap /swapfile

Setting up swapspace version 1, size = 5 GiB (53687055024 bytes)
no label, UUID=ead1f.....

• Enable the swap file
  You need to enable the swap file so that your system know it can use this file as swap.

sudo swapon /swapfile

• Vertify

free -m

• Disable files for swapping (When You Don’t Need This Swap File AnyMore)

sudo swapoff <swap>

• Enable swap from the next boot
  Insert the following line in /etc/fstab for swap from the next boot:
  <swapfile> none swap defaults 0 0
  You can do it manualy or use the command line:

echo '/<swapfile> none swap fefaults 0 0' | sudo tee -a /etc/fstab

Approach 2 – Create swap partition

• Create a new partition
  Please check out the article about Expand virtual hard disks on Linux VM
• Format and create swap space

sudo mkswap /dev/sda2

※Warning：The mkswap command will format a partition for swap space.

• Enable the swap partition

sudo swapon /dev/sda2

• Verify

free -m

• Disable partitions for swapping (When You Don’t Need This Swap Partition AnyMore)

sudo swapoff <swap>

• Enable swap from the next boot
  Insert the following line in /etc/fstab for swap from the next boot:
  <swappartition> none swap defaults 0 0
  You can do it manualy or use the command line:
  echo ‘/<swappartition> none swap fefaults 0 0’ | sudo tee -a /etc/fstab