How can I create a swap file?

I know how to create and use a swap partition but can I also use a file instead?

How can I create a swap file on a Linux system?

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Answers:

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Method 1

I myself have on several machines a swap file on mdadm RAID, therefore there’s a bit of overhead. But anyway, if you adjust vm.swappiness wisely to a more acceptable value than 60, which is the default, you should have no problem.

For instance, I have 32GB RAM server with 32GB swap file on RAID6 with vm.swappiness = 1. Quoting the Wikipedia:

vm.swappiness = 1: Kernel version 3.5 and over, as well as Red Hat kernel version 2.6.32-303 and over: Minimum amount of swapping without disabling it entirely.

In this example, we create a swap file:

8GB in size
Located in /raid1/

Change these two things accordingly to your needs.

Open terminal and become root (su); if you have sudo enabled, you may also do for example sudo -i; see man sudo for all options):
```
sudo -i
```

Allocate space for the swap file:

dd if=/dev/zero of=/raid1/swapfile bs=1G count=8

Optionally, if your system supports it, you may add status=progress to that command line.

Note, that the size specified here in G is in GiB (multiples of 1024).

Change permissions of the swap file, so that only root can access it:
```
chmod 600 /raid1/swapfile
```
Make this file a swap file:
```
mkswap /raid1/swapfile
```
Enable the swap file:
```
swapon /raid1/swapfile
```
Verify, whether the swap file is in use:
```
cat /proc/swaps
```
Open a text editor you are skilled in with this file, e.g. nano if unsure:
```
nano /etc/fstab
```
To make this swap file available after reboot, add the following line:
```
/raid1/swapfile        none        swap        sw        0        0
```

Method 2

$ sudo fallocate -l 1G /swapfile
$ sudo dd if=/dev/zero of=/swapfile bs=1024 count=1048576
$ sudo chmod 600 /swapfile
$ sudo mkswap /swapfile
$ sudo swapon /swapfile

Editor’s note: Step 1 and Step 2 are interchangeable.

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0

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