A main function of a RAM disk is application caching folder. There are two main types of RAM Disk, which is used in linux.

(1)ramfs
(2)tmpfs

Check the free RAM on linux machine using through free command

Create a folder to use as a mount point for your RAM disk.

mkdir /ramdisk

Use mount command to use create ram disk and mount .

mount -t [TYPE] -o size=[SIZE] [FSTYPE] [MOUNTPOINT]

For example like below :

mount -t tmpfs -o size=8000M tmpfs /home/ramdisk/

[TYPE] RAM disk type.
[SIZE] is the size to use for the file system.
[FSTYPE] Type of RAM disk to use .

In the example [TYPE] of ramdisk , size of Ramdisk which will used for ramdisk. type of ram disk like ext4, ext3, tmpfs.