Quick HOWTO: Reduce SWAP Partition Online without reboot in Linux

Recently I had a request to reduce the swap space and allocate that space to some other LV in one of our server.  Below is what I followed and it perfectly worked for me.  :)

Make sure you have enough physical memory to hold the swap contents. 

Now, turn the swap off:

# sync

# swapoff <YOUR_SWAP_PARTITION>

Now check the status

# swapon -s 

Then, Use fdisk command:

# fdisk <YOUR_HARDDISK_Where_SWAP_Resides>

List partitions with "p" commandFind Delete your partition with "d" commandCreate a smaller Linux-Swap partition with "n" commandMake sure it is a Linux-Swap partition (type 82) (Change with "t" command)Write partition table with "w" command

Run "partprobe" to update Filesystem table to kernel. (It is very important before proceeding further)

Then,

mkswap <YOUR_NEW_SWAP_PARTITION>

swapon <YOUR_NEW_SWAP_PARTITION> 

check to make sure swap is turned on

swapon -s 

Now you can use your free space to increase space for other Logical volumes (LV). 

Use fdisk command to create new partition, then 

# partprobe

# pvcreate <NEW_PARTITION_YOU_CREATED>

# vgextend <VG_TO_INCREASE> <YOUR_NEW_PV>

# lvextend -L  +SIZE_TO_INCREASE <LV_NAME> 

Note: It is extreme importance of syncing and turning the swap off before you change any partitions. If you FORGET TO DO THIS, YOU WILL LOST_DATA!!

Clear Swap Space in Linux

There have been times where it has been necessary for UNIX Admins to clear out the swap space on a Linux system. In order to do this, you must first make sure that you have enough free memory to hold what is being used by swap.


First we want to see what is currently being used.

free

Then I run the actual commands that empty the swap:

swapoff -a and then swapon -a

Then I check what is being used after doing this.

free