How to create swap file

 

How to Create, Verify, and Increase Swap Space on Linux

Swap space is disk space that Linux uses as virtual memory when physical RAM is exhausted. Proper swap configuration helps improve system stability and prevents out-of-memory situations.

PURPOSE: All documents are provided on this Blog just for educational purposes only.  Please make sure that you run it in your test environment before to move on to production environment. 

What is Swap Space?

Swap is a reserved area on disk that acts as an extension of RAM. When memory usage becomes high, inactive pages can be moved from RAM to swap, freeing memory for active processes.

Benefits of Swap

• Prevents application crashes due to memory shortages.
• Provides additional virtual memory.
• Supports system hibernation (when configured appropriately).
• Improves system stability during memory spikes.

Check Existing Swap Space

Use any of the following commands to verify current swap configuration and usage.

free -h

Check Active Swap Devices

swapon -s

cat /proc/swaps

swapon --show

Create a New Swap File

This method creates a 2 GB swap file. Adjust the size according to your requirements.

Step 1: Disable Existing Swap (if required)

swapoff -a
Step 2: Create Swap File
sudo fallocate -l 2G /swapfile
Verify file creation:
ls -lh /swapfile

Step 3: Set Correct Permissions
sudo chmod 600 /swapfile
Verify permissions:
ls -l /swapfile
Step 4: Format the File as Swap
sudo mkswap /swapfile

Step 5: Enable Swap
sudo swapon /swapfile

Step 6: Verify Swap Activation
swapon --show
or
free -h

Step 7: Make Swap Persistent After Reboot
Add the following entry to /etc/fstab:
echo "/swapfile none swap sw 0 0" | sudo tee -a /etc/fstab
Verify:
cat /etc/fstab
Expected entry:
/swapfile none swap sw 0 0

Increase Existing Swap Partition
Current swap size: 8GB
Target swap size: 16GB

Step 1: Disable Swap
swapoff -a
Verify:
swapon --show
No output should be displayed.
Step 2: Increase Virtual Disk Size in vCenter
Increate hard disk 1 from 64 to 90 GB
Navigate to VMware vCenter:
VM Settings
→ Hard Disk 1
→ Increase disk size
Example:
64 GB → 90 GB

Step 3: Detect New Disk Size
Check available disk space:
fdisk -l
If the new size is not visible, rescan the disk:
echo 1 > /sys/class/scsi_device/0\:0\:0\:0/device/rescan
Run again:
fdisk -l

Step 4: Modify Partitions
Launch partition manager:
cfdisk
Existing Layout
/dev/sda3  Linux filesystem
/dev/sda4  Linux swap
Delete Existing Swap Partition
Select:
/dev/sda4
Choose:
Delete
Resize Root/Data Partition 
cfdisk
Select:
/ dev/sda3  # This was a root partition which we increased on vCenter.
Choose:
Resize ==> Write

Create New Swap Partition
Use remaining free space:
New
Type → Linux swap

mkswap /dev/sda4
Setting up swapspace version 1, size = 26 GiB (27917262848 bytes)
no label, UUID=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx
# edit the UUID
vi /etc/fstab

mount -a

swapon /dev/sda4
swapon --show
NAME      TYPE      SIZE USED PRIO
/dev/sda4 partition  26G   0B   -2