Thanks! But how can I test the swap effectiveness?

You can see the swap summary with the command “swapon -s”

ohhh god!!! thanks!!!

Do we have to reboot after swapon /swapfile ?

no reboot is necessary after the swapon command.

What is the > bs=1024 count=512k < in the above command?

How do we set the size? for example if I’m running on a 256mb plan

C

BS stands for blocksize and in this case it will be 1,024 bytes. Count is how many times to write this block, or 512,000 * 1,024 bytes = 512MB of SWAP

Thank you guys! That’s very useful!

Please note that for security reasons it is advisable to enter something like:

chown root:root /swapfile

chmod 0600 /swapfile

source: http://www.cyberciti.biz/faq/linux-add-a-swap-file-howto/

Thanks, Andrea, I have added that to the tutorial!

For anyone who wants to increase their swapsize after they have followed this tutorial you can follow the below steps. With the increase in memory on the base packages from 256MB to 512MB, I wanted to create a swap file double the “physical” memory size ie 1GB instead of the 512MB made in this tutorial:

1. Turn the swapfile off : swapoff -a
2. sudo dd if=/dev/zero of=/swapfile bs=1024 count=1024k
3. Follow the remaining steps from after the dd command. Except for the Fstab modification as that is already completed.
4. Your swapfile is now bigger

Minor suggestion is that you need sudo before those last two chown/chmod commands and I noticed the dd command took a few minutes so it would be reassuring to note this to avoid worry that something has gone wrong!

That’s correct you will want to either use sudo or do this as root.

And the dd command is writing directly to disk so it will take a bit of time depending on the size of the swapfile that is written.

Thanks for pointing that out.

Thanks, this worked great. You can see how much swap is being used by entering top -c right below the memory usage. Have yet to see my server use the swap - but its there if it needs it and its great that DigitalOcean uses a SSD so the swap should be quicker than other hosts.

Is there a downside to setting the swap to be very large? I have 2GB of memory and my site takes ~100mb… so would it be bad to have a 4GB swap?

Thanks for your article. My web site’s db (mysql) drop 3 - 4 times, i hope it will help

@danafrancey The only downside is that you use more diskspace for swap, and you probably don’t need to…

Optionally, to change the swappiness of the system, edit /etc/sysctl.conf And add a line at the bottom: vm.swappiness=20 Then type: sysctl -p This sets the system to swap memory only when RAM usage is more than 80%, default was swapping when RAM usage was more than 60%, which results in most of the services being swapped if you experience a traffic spike.

Tiny detail: The number 262140 found twice in the article should really be 524284 :-)

Good one

when can i see any memory been swapped?

30 mins after setting this and I type free command:

         total       used       free     shared    buffers     cached

Mem: 508396 501272 7124 0 20472 340460 -/+ buffers/cache: 140340 368056 Swap: 524284 0 524284

You can use fallocate instead of dd to speed up the file creation - instead of manually writing each 0 like dd does, it just makes the container of the file:

fallocate -l 512M /swapfile

is equivalent to

dd if=/dev/zero of=/swapfile bs=1M count=512

and takes under a second or two to execute.

Great tutorial! Luckily, I stumbled onto it by accident. For the benefit of other future newbies, a link to this tutorial should be referenced in other rudimentary HowTos… just a suggestion.

silly but can u have more than 1 swap file? i mean… can i have like… 5 swap files using 30% of my host space? buddy press is memory hungry :(

Disadvantages section : "Because hard disks have a much slower memory than RAM, virtual private server performance may slow down considerably. "

But DigitalOcean uses a SSD , not hard drive. So this statement is useless.

What exactly does a droplet use swap for, and how much is optimal?

Thanks

@leo: You shouldn’t have more than 1 swap file - you should instead increase the size of your swap file.

@yangyun: It’s not useless - even SSDs are still slower than RAM.

As per the article:

Linux RAM is composed of chunks of memory called pages. To free up pages of RAM, a “linux swap” can occur and a page of memory is copied from the RAM to preconfigured space on the hard disk. Linux swaps allow a system to harness more memory than was originally physically available.

In case of debian you might have to run the command ‘swapon’ with ‘sudo’, otherwise it might return “command not found”.

Or use ‘/sbin/swapon -s’ mostly because /sbin is not added to the PATH of a normal user by default.

@kadaj: Thanks! I’ve updated the article.

Super easy and worked perfectly. Capistrano wasn’t deploying because it said I didn’t have enough RAM to precompile my assets ["Rake aborted! Cannot allocate memory - nodejs … ]. Enabled 1GB swap file. Voila, problem solved.

Thanks!

Thanks a lot, mysql was falling down like ones a week until I discover the reason via nagios.

i really dont know how to do as below mention. can anyone rewrite it in more detail method?

Optionally, to change the swappiness of the system, edit /etc/sysctl.conf And add a line at the bottom: vm.swappiness=20 Then type: sysctl -p This sets the system to swap memory only when RAM usage is more than 80%, default was swapping when RAM usage was more than 60%, which results in most of the services being swapped if you experience a traffic spike.

@nhatkhoa: This is a one-line command of the mentioned section :]

<pre>echo “vm.swappiness=20” | sudo tee -a /etc/sysctl.conf && sudo sysctl -p</pre>

Is it possible to Create LVL Partion for Snapshots same way ?

Does anybody else get “swapon: /swapfile: swapon failed: Device or resource busy” when following this tutorial on Ubuntu 13.04?

@eli.xir: Unfortunately that’s not possible.

@gwilymgj: Does /swapfile already exist? <pre>stat /swapfile</pre>

thanks

thanks

great tutorial :)

Is there any way to have encrypted swap? The instructions I’ve seen includes mounting the swapfile as a loop device, which isn’t supported by the vm (or so it seems).

@Klaus: Have you tried this? <a href=“http://askubuntu.com/questions/248158/how-do-i-setup-an-encrypted-swap-file”>http://askubuntu.com/questions/248158/how-do-i-setup-an-encrypted-swap-file</a>

I noticed when I reboot my machine (for an image creation), the swap file vanishes and I have to go through this process again.

I’m fine just using a cron job to automate it, but am I doing something wrong?

@shade: It shouldn’t just “vanish”. Can you please try it on a fresh new droplet and see if you can replicate it?

Thank you very much.

sysctl -w vm.swappiness=0

Excellent article. My MySQL kept crashing due to ‘out of memory’ issues. Hopefully this will solve it.

Couldn’t change swappiness with the tutorial method brian’s comment above worked. sysctl -w vm.swappiness=0

I’m very new to this and am therefore following the instructions literally. On a fresh install dual boot with win 7 Pro x64 I’ve installed Ubuntu 12.04 LTS and all seems to be working. Checked that there was no swap file (cannot create a 5th partition so will be using a file). Entered the above command line sudo dd if=/dev/zero of=/swapfile bs=1024 count=8192k except made the swap file the size of the RAM. It took a bit and then returned 8388608+0 records in 8388608+0 records out 8589934592 bytes (8.6 GB) copied, 71.4647 s, 120 MB/s

So far so good. I typed sudo mkswap /swapfile and the response was /swapfile: No such file or directory

So I figure there is an assumption somewhere that I’ve missed. Any advice would be appreciated.

@dlingen: I don’t recommend using a swapfile too large because it might actually decrease performance. 512MB is usually enough. Make sure that /swapfile exists: <pre>stat /swapfile</pre>