What is Swapping?
In modern Operating Systems, program which is accessed less frequently can be temporarily stored on disk or other media, So that this space can be used by some other program which really need it.This is called "swapping", as an area of memory that can be used by others and what this contains can be swapped or exchanged easily. Swapping is also known as "Paging".
Features of Swapping:
Mainly, Swapping has two important features:
1. Useful for executing the programs which need memory more than available physical memory. In these scenarios, Kernel/OS move out less used programs from main memory and move in the process that needs memory immediately to memory.
2. Any, application which loads number of pages during its startup and then don't use those ones any more. Now such unused pages can be stored in swap space, so that main memory can be freed for other programs.
Swap Space in Linux-
In Linux, normally during installation we create swap partition(used for swapping purpose). Mostly, we create swap partition/file of size equal to 2*sizeof(RAM). This is because we need almost double space while doing swapping for any program(hope you already know this, not going in details).
Note : On system where we have enough RAM present to handle memory requirements for all processes, we don't need to create swap partition/file twice of RAM. As, this will not be fully utilized and will be wastage of space.
How to free/clear the Swap Partition/File when gets filled up?
Now, let us come to main topic. Suppose any time due to number of swap in/out your all space gets utilized and you want to free up swap partition/file. In that case you can follow below steps.
You may be wondering that I am using two terms partition and file. So, Partition is logical portion of our HDD and file is the special file that we have created on existing partition that can be used for swapping .
To check what swap space you have. you can use "swapon -s" as root.
# swapon -s
Filename Type Size Used Priority
/dev/sda3 partition 4096564 308 -1
Here, Type field indicate that we have swap space as "Partition" rather than file and logical partition is "/dev/sda3". Size column show the size in "KB", Used column shows How many space has been used in "KB" and finally Priority columns tell kernel to which swap space is to be used first.
Currently, I have 308 KB of swap space is used and I want to free up all the used space. But, before clearing you used swap space, make sure you have enough free main memory to hold the pages which currently reside in space space. In, my case I have enough free memory to hold pages in swap space. So, I am moving ahead with this :).
#free -o
total used free shared buffers cached
Mem: 49453924 49002192 451732 0 1547144 24390976
Swap: 4096564 308 4096256
# swapoff -a && swapon -a# free -o
total used free shared buffers cached
Mem: 49453924 49002572 451352 0 1547816 24391608
Swap: 4096564 0 4096564
Note : Time taken to free up your swap space depends on the size of your swap partition/file. More is the size, more will be the time taken to free up space.
Hope this will help you!!
Thanks! !
