Debian: Setting up a swap file in Debian instead of a separate partition

Swap (swap file) is a special area on the disk that the operating system uses when physical RAM becomes insufficient. Although modern systems often have large amounts of RAM, swap can still be useful. Even with sufficient RAM, it is advisable to have a small swap (e.g., 1-2 GB) as a backup. Historically, the swap partition was placed at the end of the disk due to the peculiarities of early file systems and disk controllers: this allowed faster allocation and use of contiguous space, as placement at the disk end (closer to the "unserviced" area) reduced fragmentation and sped up access, especially on HDDs, where write speed decreases towards the center of the disk, but often there was more free space at the end without affecting the root and system partitions at the beginning. In modern realities and with virtualization use, it has become inconvenient to expand the disk and file system when necessary if a swap partition exists at the end of the disk. Therefore, this partition can be removed, and swap can be used as a file on the main partition.

To reconfigure, follow these steps:

1. Before creating a swap file, check how your swap is currently configured:
sudo swapon --show
or
free -h

2. Ensure you have enough free disk space:
df -h

It is recommended to leave at least 5% of free space on the partition after creating the swap file.

3. Create the swap file using the "dd" utility:
sudo dd if=/dev/zero of=/swapfile bs=1M count=2048 status=progress

where
bs=1M — block size of 1 MB;
count=2048 — number of blocks (resulting size: 2048 MB ≈ 2 GB);
status=progress — shows progress (not available in all versions of dd).

IMPORTANT!!! The recommended swap size is often from 50% to 100% of the RAM amount, but no more than twice. However, for modern systems with a large amount of RAM (16 GB or more), 2-4 GB of swap is often sufficient unless you plan to use hibernation (then the swap size should be no less than the amount of RAM).

4. Restrict access to the file to only root:
sudo chmod 600 /swapfile

5. Format the file for swap:
sudo mkswap /swapfile

6. Activate swap:
sudo swapon /swapfile

7. Verify that swap is active:
sudo swapon --show
or
free -h

8. Disable the swap partition (/dev/sda3):
sudo swapoff /dev/sda3

9. Reconfigure "/etc/fstab" for correct automatic mounting of the swap file at system boot. To do this, open "fstab" for editing, find a line like:
UUID=9f3c3eb7-dbc0-45ca-9299-5bb6f9ae8958 none swap sw 0 0

Change "UUID=9f3c3eb7-dbc0-45ca-9299-5bb6f9ae8958" in the line to "/swapfile" and save the configuration file.

10. Now delete the "/dev/sda3" partition and expand the main "/dev/sda2" partition using the "fdisk" utility:
sudo fdisk /dev/sda

Enter "p" to view the partition list. Next, enter "d" and select the partition number where the swap was previously located. Check with "p" whether the correct partition was deleted. To save changes, enter "w"; to exit and cancel changes in case of an error, enter "q".

11. Expand your main partition using the freed disk space. Inside the "fdisk" utility, enter the command "e", specify your partition number, indicate how much to increase it. Exit the utility with the "w" command.

12. Finally, expand the file system of the main partition:
sudo resize2fs /dev/sda2

13. Check the changes with the commands:
lsblk -l
df -h