Good way to add a swap file (like windows does) if you forget to create them during install
Create the swap file using fallocate
fallocate program is a best way to create a file of a preallocated size instantly.
The following command will create 1GB of /swapfile.
$ sudo fallocate -l 1G /swapfile
Check whether its created correct size of file or not.
$ ls -lh /swapfile -rw-r--r-- 1 root root 1.0G Jun 7 09:49 /swapfile
Change the file permission to 600 to only accessible by root user.
$ sudo chmod 600 /swapfile
Convert the file as swap area by running below command.
$ sudo mkswap /swapfile Setting up swapspace version 1, size = 1024 MiB (1073737728 bytes) no label, UUID=cda50e0e-41f3-49c7-af61-b8cb4a33a464
Enable the swap file by running below command.
$ sudo swapon /swapfile
Add newely created swap file into fstab file, so that swap space partition available even after the reboot.
$ vi /etc/fstab /swapfile swap swap defaults 0 0
Check newly created swap file.
$ swapon --show NAME TYPE SIZE USED PRIO /dev/sda5 partition 2G 657.8M -1 /swapfile file 1024M 0B -2
Yes i can see the new 1GB swapfile. Reboot the system to use the new swap file.