Design Hard Disk Layout Manage Swap Space

In this lesson we’ll explore how to configure and manage swap space in Linux. Swap is a dedicated area on disk where the kernel moves inactive pages from RAM when physical memory is exhausted. We’ll cover both swap partitions and swap files, with step-by-step examples.

Understanding Swap with a Simple Scenario

Imagine a system with 4 GiB of RAM:

A video editor consumes 2 GiB.
An audio editor consumes another 2 GiB.

At this point, RAM is full. With a 2 GiB swap partition, Linux can relocate the idle video editor’s memory pages to swap, freeing up 2 GiB of RAM for a new application such as Chrome.

The image illustrates the concept of managing swap space, showing a 4GB RAM with 2GB used by an audio editor and Chrome, and a 2GB swap partition used by a video editor.

Note

Swap space is much slower than RAM. Use it as overflow memory, not as a substitute for adequate physical RAM.

Checking Existing Swap

List active swap areas:

swapon --show

Inspect block devices and partitions:

lsblk

Example output:

NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
vda      8:0    0   20G  0 disk 
├─vda1   8:1    0    1G  0 part /boot
├─vda2   8:2    0   19G  0 part 
│ ├─cs-root 253:0 0   17G  0 lvm  /
│ └─cs-swap 253:1 0    2G  0 lvm  [SWAP]
vdb      8:16   0   10G  0 disk 
├─vdb1   8:17   0    1G  0 part 
├─vdb2   8:18   0    4G  0 part 
└─vdb3   8:19   0    2G  0 part

In this example, /dev/vdb3 is reserved for swap but not yet active.

Command Reference

Task	Command
List active swap	`swapon --show`
List block devices	`lsblk`
Format a swap partition	`sudo mkswap /dev/vdb3`
Enable a swap area	`sudo swapon --verbose /dev/vdb3`
Disable a swap area	`sudo swapoff /dev/vdb3`
Create a swap file (2 GiB)	`sudo dd if=/dev/zero of=/swap bs=1M count=2048`
Secure swap file permissions	`sudo chmod 600 /swap`
Format a swap file	`sudo mkswap /swap`
Enable swap file	`sudo swapon --verbose /swap`

Creating and Enabling a Swap Partition

Format the partition:
```
sudo mkswap /dev/vdb3
```
Activate it immediately:
```
sudo swapon --verbose /dev/vdb3
```
Verify it’s active:
```
swapon --show
```
Make it persistent by adding to /etc/fstab:
```
/dev/vdb3 none swap sw 0 0
```

Disabling Swap

To turn off a swap partition or file:

sudo swapoff /dev/vdb3

Creating and Using a Swap File

If you cannot repartition the disk, create a swap file instead:

Create a zero-filled file (2 GiB):

sudo dd if=/dev/zero of=/swap bs=1M count=2048 status=progress

Restrict permissions:
```
sudo chmod 600 /swap
```
Format the file as swap:
```
sudo mkswap /swap
```
Enable the swap file:
```
sudo swapon --verbose /swap
```
Persist across reboots by adding to /etc/fstab:
```
/swap none swap sw 0 0
```

Warning

Excessive swapping (thrashing) can severely degrade performance. Monitor swap usage with free -h, vmstat, or htop.

Links and References

Practice these commands to master swap space management on Linux.

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