How to add swap memory on AlmaLinux 8.5

What is swap space/memory?

When the amount of physical memory (RAM) is full, swap space in Linux is used. Non-active pages in memory are moved to the swap memory if the system requires more memory resources and also the RAM is complete.

While swap memory can help devices with a percentage of RAM, it should not be thought about a substitute for more RAM. Swap memory is located on hard disk drives, which have a slower accessibility time than physical memory.

What is the formula to calculate the required swap memory?

The swap space ought to amount to 2x physical RAM for approximately 2 GB of physical RAM, and after that an extra 1x physical RAM for any kind of amount over 2 GB, yet never ever less than 32 MB.

For systems with actually big amounts of RAM (more than 32 GB), you can likely get away with a smaller swap partition (around 1/2 half the physical RAM).

Formula:

# MEMORY = Amount of RAM in GB.
# SWAP_MEMORY = Amount of Swap Memory in GB.

if MEMORY < 2:
   SWAP_MEMORY = MEMORY * 2
elif MEMORY > 32:
  SWAP_MEMORY = MEMORY / 2
else:
  SWAP_MEMORY = MEMORY

Using this formula:

A system with 2 GB of physical RAM would certainly have 4 GB of swap memory.

A system with 3 GB of physical RAM would certainly have 3 GB of swap memory.

A system with 64 GB of physical RAM would certainly have 32 GB of swap memory.

If you intend to upgrade your RAM at a later time, creating a huge swap space partition can be particularly practical.

Identifying current swap space

Before you start, check if your AlmaLinux installation already has swap enabled by typing: cat /proc/swaps

[root@krython ~]# cat /proc/swaps
Filename                                Type            Size    Used    Priority
/dev/dm-1                               partition       2248700 0       -2

Alternatively, use the swapon --show command:

[root@krython ~]# swapon -s
Filename                                Type            Size    Used    Priority
/dev/dm-1                               partition       2248700 0       -2

Finally, the free command may also be used:

[root@krython ~]# free
              total        used        free      shared  buff/cache   available
Mem:         828588      154880      465120        5640      208588      544820
Swap:       2248700           0     2248700

In the first two commands if the result is empty it means that your system does not have swap space enabled.

In the last command if the result of the Swap (the total column) is 0 it means that your system does not have swap space enabled.

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NOTE: A System may have multi swap partitions

Creating the swap file

The user that you are logged in as must be a root user or should have sudo privileges to be able to create and add swap space.

In this tutorial, we will add 2GB of Swap memory to our AlmaLinux System.

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Note: Replace the 2G with the size of the swap memory you need.
Example: 12G if you want a 12GB of Swap space

Let's begin:

Create a swap-space folder in the main directory:

sudo mkdir /swap-space

Install the fallocate command, we will use it to create the swap file:

sudo dnf install util-linux -y

Create the swap file inside the swap-space folder that will be used as a Swap space:

sudo fallocate -l 2G /swap-space/swapfile

Ensure that only the root user can read and write the swap file by setting the correct permissions:

sudo chmod 600 /swap-space/swapfile

Configure the file as swap:

sudo mkswap /swap-space/swapfile

Activate the swap space A temporary activate (lost on reboot):

sudo swapon /swap-space/swapfile

Finally, modify the /etc/fstab to automatically add the new swap at system boot time (We will use nano editor):

sudo nano /etc/fstab

if nano isn't already installed on your system!

sudo dnf install epel-release -y && sudo dnf install nano -y

After opening the /etc/fstab file with nano, paste the following line:

/swap-space/swapfile swap swap defaults 0 0

Save & Exit with (ctrl+x) then type: y then hit enter

Verify that the swap is active by using either the swapon or the free command:

[root@krython ~]# sudo swapon -s
NAME                 TYPE      SIZE USED PRIO
/swap-space/swapfile partition 2.1G   0B   -2

[root@krython ~]# free -m
              total        used        free      shared  buff/cache   available
Mem:            809         160         258           5         389         521
Swap:          2195           0        2195

What is swappiness and how do I change it?

The swappiness parameter controls the tendency of the kernel to relocate processes out of physical memory and onto the swap disk. This can lead to slower response times for systems and also applications if processes are too strongly moved out of memory due to the fact that disks are much slower than RAM.

swappiness can have a value of between 0 as well as 100
swappiness=0 tells the kernel to avoid swapping processes out of physical memory for as long as feasible
swappiness=100 informs the kernel to boldy swap processes out of physical memory as well as relocate them to swap cache

The default setup in AlmaLinux is swappiness=30.

Lowering the default value of swappiness will possibly boost general performance for a regular AlmaLinux desktop setup.

A value of swappiness=10 is suggested, yet feel free to experiment.

Keep in mind: AlmaLinux server installations have different efficiency requirements to desktop computer systems, and also the default value of 30 is likely more suitable.

Check the swappiness value:

cat /proc/sys/vm/swappiness

Change the swappiness value A temporary change (lost on reboot):

sudo sysctl vm.swappiness=60

Make the change permanent, edit the configuration file located in /etc/sysctl.conf

sudo nano /etc/sysctl.conf

Search for vm.swappiness and change its value as desired. If vm.swappiness does not exist, add it to the end of the file like so:

vm.swappiness=60

Save & Exit with (ctrl+x) then type: y then hit enter

Finally, reboot your system:

sudo reboot

Empty the swap space

Even if you have lots of RAM and also even if you have a reduced swappiness value, it is possible that your computer swaps. This can injure the multitasking efficiency of your desktop computer system.

You can use the following script to get the swap manually back into RAM:

sudo nano /usr/local/sbin/s2m.sh

Copy and paste the script into the file:

#!/bin/sh

mem=$(LC_ALL=C free  | awk '/Mem:/ {print $4}')
swap=$(LC_ALL=C free | awk '/Swap:/ {print $3}')

if [ $mem -lt $swap ]; then
    echo "ERROR: not enough RAM to write swap back, nothing done" >&2
    exit 1
fi

swapoff -a &&
swapon -a

Save & Exit with (ctrl+x) then type: y then hit enter

Grant the script executable permissions:

sudo chmod +x /usr/local/sbin/s2m.sh

Run it

sudo /usr/local/sbin/s2m.sh

Remove a swap file

You will do the opposite steps of the installation process, deactivate then remove the swap file

Deactivating the swap space:

sudo swapoff -v /swap-space/swapfile

Remove the swap file entry from the /etc/fstab file:

sudo nano /etc/fstab

# remove the line --> /swap-space/swapfile swap swap defaults 0 0

Save & Exit with (ctrl+x) then type: y then hit enter

Finally, Delete the swap folder and the swap file:

sudo rm -rf /swap-space

Conclusion

You have learned how to create a swap file and also activate it on your AlmaLinux system.

You have learned how to change the swappiness value on your AlmaLinux system.

You have learned how to deactivate swap space as well as remove your swap file on your AlmaLinux system.