Shared from https://sharadchhetri.com/2014/12/01/create-new-swap-file-centos-7-rhel-7/

In this tutorial we will learn how to create new swap file on CentOS 7 / RHEL 7. Generally on Cloud Servers ( AWS/ DigitalOcean) or VPS, swap space is not created by default. This requirement we can achieve within a few steps.

Prerequisites

Must have free space on mounted disk. You can check by using df -Th command.

Steps to create / add new swap file on Linux

1. Create swapfile-additional file with dd command in / (root). You can select any other partition but it should be mounted (For eg. /opt, /usr ,/NewMountedPartition)

dd if=/dev/zero of=/swapfile-additional bs=1M count=4048

dd = It is a unix command used for convert and copy a file
if = read from FILE instead of stdin
/dev/zero = /dev/zero is a special file in Unix-like operating systems that provides as many null characters (ASCII NUL, 0x00) as are read from it
of = write to FILE instead of

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