Create a swapfile for your Linux server

[Discourse]

For servers with <= 4GB of RAM, running ./discourse-setup will prompt for and automatically create a 2GB swapfile.

Most cloud virtual machine providers do not set up swapfiles as part of their server provisioning.

In particular, upgrading Discourse produces a lot of memory pressure. With a swap file, rather than randomly terminating processes with an out of memory error, things will slow down instead. Having a swap file is a cheap insurance policy that protects you from many other load related failures.

This can be done at any time from the command line on your server.

Set up a 2GB swap file

We recommend a 2GB swap file for Discourse, unless your server has more than 4GB of memory.

In the shell you have opened to your droplet, do the following:

You will need to be root for much of this, so either be root or sudo -s before running these commands! Don’t forget to exit root afterwards.

1. Create an empty swapfile

    install -o root -g root -m 0600 /dev/null /swapfile
   

2. Allocate a 2GB file named ‘swapfile’

    fallocate -l 2G /swapfile
   

3. tell linux this is the swap file:

    mkswap /swapfile
   

4. Activate it

    swapon /swapfile
   

5. Add it to the file system table so its there after reboot:

    echo "/swapfile       swap    swap    auto      0       0" | tee -a /etc/fstab
   

6. Set the swappiness to 10 so its only uses as an emergency buffer

    sysctl -w vm.swappiness=10
    echo 'vm.swappiness = 10' > /etc/sysctl.d/30-discourse-swap.conf
   

The whole thing as a single copy and pastable script:

install -o root -g root -m 0600 /dev/null /swapfile
fallocate -l 2G /swapfile
mkswap /swapfile
swapon /swapfile
echo "/swapfile       swap    swap    auto      0       0" | tee -a /etc/fstab
sysctl -w vm.swappiness=10
echo 'vm.swappiness = 10' > /etc/sysctl.d/30-discourse-swap.conf

Last edited by @JammyDodger 2022-05-23T18:45:59Z

Check document

Perform check on document:

[nathank (Nathan Kershaw)]

I’ve been trying to set up a larger swapfile (4GB instead of the default 2GB), but have run into this when running the script above:

rm: cannot remove `swapfile’: Operation not permitted

To get around this, I’ve had to do this first:

1. Reboot the server (it wouldn’t let me swapoff, presumably due to heavy swapfile use)
2. swapoff -a -v

[Ed_S]

@nathank

I’ve been trying to set up a larger swapfile

For similar reasons, I run with two swapfiles:

# swapon
NAME                       TYPE  SIZE  USED PRIO
/var/local/swap/swapfile.0 file 1024M 44.9M   -3
/var/local/swap/swapfile.1 file 1024M 1024M   -2

[pfaffman (Jay Pfaffman)]

A second swap file could be a clever way to avoid the reboot. Just create a second swap file, enable it, and then remove the first.

[NateDhaliwal]

Значит, нам не нужно следовать этой инструкции для создания файла подкачки размером 2 ГБ, поскольку установка делает это автоматически, если у нас меньше 2 ГБ памяти?

[Ed_S]

@Nate Dhaliwal

Установка уже делает это

Да, но если вы измените конфигурацию сервера или, возможно, выполните миграцию, вам, возможно, придется позаботиться об этом самостоятельно. (В то же время есть две важные конфигурации ядра, которые необходимо изменить, и установка не занимается ими — см. Мнение MKJ о конфигурации развёртывания Discourse)