How to create Swap File for Linux


One of many really helpful methods of boosting your server’s efficiency and avoiding working out of reminiscence is by making a swap house or swap file. Swap is digital reminiscence situated in your onerous disk and extends the RAM when the reminiscence utilization is excessive.

When your system is working out of the primary reminiscence, the Linux kernel swaps a portion of reminiscence from the RAM and writes it onto the onerous disk. This fashion, extra RAM is made out there to the system and processes can run easily.

On this tutorial, we discover ways to create a swap file on Linux distributions similar to Ubuntu and CentOS.

Verify swap configured

Having checked out some great benefits of making a swap file, it is essential to first affirm if swap is configured in your system. It will enable you to to know whether or not or to not configure a swap file.

To verify if swap house is created, run the next command :

$ swapon

The command will show the dimensions of the swap partition and the filesystem label. This is some output of the command.

/dev/sda9 partition 3.8G 383.3M -2

In case you run the command and also you get no output, then it implies that you do not have a swap partition configured. You possibly can affirm the absence of swap house by working the next command:

$ free -h

This shows the statistics of the primary reminiscence and swap utilization.

whole used free shared buff/cache out there
Mem: 7.6G 5.6G 386M 1.1G 1.7G 675M
Swap: 0B 0B 0G

From the output, we will clearly see that within the ‘swap’ row, no reminiscence is printed. It is a affirmation that there is not any lively swap partition residing on the Linux system. Let’s now create a swap file for the system.

Verify onerous disk house

As earlier mentioned, swap house is digital reminiscence residing on the onerous disk that gives an extension to the RAM. With that in thoughts, we’re going to create a swap file on the onerous disk. However earlier than we achieve this, it is all the time prudent to verify the out there onerous disk house.

To verify the out there onerous drive house on Linux, run the next command:

$ df -h

Within the output, be looking out for the basis partition denoted by a single forward-slash ( / ) below the ‘Mounted on’ column. Within the output beneath, the basis partition is labeled as /dev/sda7 filesystem and has 97G free house which is greater than sufficient.

Filesystem Measurement Used Avail Use% Mounted on
udev 3.9G Zero 3.9G 0% /dev
tmpfs 784M 2.3M 781M 1% /run
/dev/sda7 156G 54G 97G 39% /
tmpfs 3.9G 828M 3.1G 22% /dev/shm
tmpfs 5.0M 4.0K 5.0M 1% /run/lock
tmpfs 3.9G Zero 3.9G 0% /sys/fs/cgroup
/dev/sda10 29G 5.9G 21G 22% /var
/dev/sda8 1.9G 124M 1.7G 7% /boot

Create a swap file

Having decided that we now have adequate house on our Linux system, we’re going to proceed with making a swap file. Keep in mind, swap house is normally created throughout set up. If swap house already exists, then you’re good to go. Nonetheless, if in case you have no swap house, it is really helpful to create a swap file.

With that in thoughts, we’re going to create a swap file of 1 GB. To attain this, subject the fallocate command as proven:

$ sudo fallocate -l 1G /swap_file

Be at liberty to provide the swap file no matter identify you want. On this case, we now have named it swap_file. Nonetheless, if the fallocate utility isn’t current, execute the next command:

$ sudo dd if=/dev/zero of=/swap_file bs=1024 depend=1048576

Subsequent, set the right file permissions for the swap file since solely the basis is allowed learn and write permissions:

$ sudo chmod 600 / swap_file

The chmod 600 argument assigns learn and write permissions solely to the swap file.

Setup swap space

To arrange the swap space, use the next command utilizing the mkswap utility as proven:

$ sudo mkswap / swap_file

To activate the swap file run the next command:

$ sudo swapon /swap_file

Making Swap Persistent on Reboot

The swap file created on the Linux system isn’t everlasting and won’t survive a reboot. To make the swap file persistent even upon a reboot, we have to edit the /and many others/fstab file and append the newly created swap entry.

Utilizing your most well-liked textual content editor, open the /and many others/fstab file. We have now used vim editor as proven:

$ sudo vim /and many others/fstab

Subsequent, paste the next content material

/swap_file swap swap defaults Zero 0

Save the adjustments and exit the /and many others/fstab file. To verify that swap file has been created run the next command:

$ sudo swapon –show

It is best to get output that’s much like what we now have

/swap_file file 1024M 346.4M -2

Swap Settings

At this level, we now have efficiently created our swap file. We’re going to contemplate another property of swap and that’s the swappiness worth. Swappiness refers to a property within the Linux kernel that determines the frequency of swap utilization.

The swappiness worth ranges from Zero to 100. A low worth implies that the system will trigger the kernel to maintain off swapping as a lot as potential. The next worth has the other impact – it makes the kernel to make use of swap as regularly as potential.

By default, the swappiness worth is 60. You possibly can affirm this by working the command:

cat /proc/sys/vm/swappiness

While this worth could appear okay, it is not most well-liked for manufacturing servers. To set a decrease worth, say 20, run the next command.

sudo sysctl vm.swappiness=20

For this worth to stay persistent upon rebooting, add the next line to the /and many others/sysctl.conf file


Swap Information vs. Swap Partitions

Linux comes with 2 sorts of swap house, swap partition and swap file. A swap partition is a definite a part of the onerous drive that’s purely used for swapping. No recordsdata exist right here.

However, a swap file is a novel file that sits on the filesystem alongside your information and system recordsdata.

Swap house actually wanted? how a lot?

The very generally requested query when putting in Linux is ‘Do I must create swap?’. As we earlier mentioned, swap house is supposed to behave as a buffer when the RAM will get exhausted for one purpose or the opposite. When there isn’t any extra reminiscence to accommodate purposes then the working system chooses a sure course of to kill. It will begin to have an effect on the efficiency of the system.

Effectively, chances are high that you could be by no means fully burn up all that RAM. Nonetheless, to be on the secure aspect, it is price having a bit swap house. Consider swap house as a security boat in a yacht. Within the unlikely occasion that the yacht catches fireplace, you need to use it to sail to security.

So right here comes the large query, How a lot swap house do I must create? To be candid, there is not a straight reply to this query, simply suggestions. RedHat’s suggestion, recommends the creation of swap house that’s 20% of the Bodily RAM put in on a Linux system. Nonetheless, this could differ relying on the dimensions of the RAM and working system.

For instance, CentOS recommends the next:

  1. If the RAM is lower than 2GB, then swap house must be twice the dimensions of RAM.
  2. If the RAM is greater than 2GB, then swap house = 2 + RAM measurement. For instance, if the RAM is Four GB, swap house must be 6 GB.

For Ubuntu, that is barely totally different

  1. If the RAM is lower than 1GB, the swap house must be equal to or double the RAM measurement.
  2. In any other case, if the RAM is greater than 1GB, swap house must be equal to the sq. root of RAM.

In hibernation mode, swap house is important for the very purpose that it preserves the state of RAM by transferring the content material situated on the RAM onto the swap partition. Because of this, it is really helpful that you just set the swap measurement to be equal to the dimensions of the RAM. so, if in case you have RAM of 8G, a swap file of 8G would suffice.


We can not emphasize extra the necessity for having swap house in your system. It turns out to be useful when the primary reminiscence is working out and lets you deal with heavy purposes similar to video modifying Software program Regardless of how giant the RAM capability is in your Linux system, it is all the time really helpful to configure swap for any unexpected occasions.

It is our hope that you could now comfortably create and allow a swap file in your Linux system. Your suggestions on this information will probably be extremely appreciated.

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