Comments on: Linux Add a Swap File – Howto

By: John Mills

John Mills — Thu, 05 Jan 2012 15:58:45 +0000

dd is a command that does a low level copy of data from a to b. ‘if’ is the input file for the copy. /dev/zero is a device that generates as many null characters as it is asked to create and passes them on. ‘of’ is your output file or what will become your new (or additional) swapfile. the ‘/swapfile’ could be any name that you want it to be as long as you don’t forget what it is for the further manipulations. ‘bs’ is the block size of the file and ‘count’ is the number of bytes in the file. So, what the command does is takes 524288 null bytes from /dev/zero and puts them into /swapfile thus initially populating the file.

By: ravinder

ravinder — Wed, 04 Jan 2012 20:15:53 +0000

dd if=/dev/zero of=/swapfile1 bs=1024 count=524288
pls tell me the meaning and function of this command..why we are using if=/dev/zero and of=/swapfile..why this command started with dd..

By: Simon McNair

Simon McNair — Thu, 27 Oct 2011 14:45:38 +0000

Hi Vivek,
5 years on and the page is still useful. Thanks :-)

By: Ron

Ron — Sun, 09 Oct 2011 07:10:27 +0000

Since kernel 2.6.31, you can use the util fallocate instead of dd on btrfs, ext4, ocfs2, and xfs filesystems. It’s *much* faster than dd on really big swap files.

By: John M

John M — Mon, 29 Aug 2011 03:09:10 +0000

You just have to:
-make sure the swap file is not active
swapon -s
-if it is active
swapoff /swapfile (or whatever you called it)
-comment out the line in your /etc/fstab file (Place a hashmark # in front of it or just delete the line)
-remove the swapfile:
rm /swapfile (or whatever you called it)

Reboot and you should be away unless you want to create a smaller swap file in which case you should just make sure it isn’t in use, delete the file and recreate it using a smaller size.

By: Adam

Adam — Thu, 04 Aug 2011 03:18:01 +0000

So, after following these steps I received the notification that my root partition is full. And then, after rebooting, I cannot log into gnome. It will start gdm but will not go into gnome from there, it will only bring me back to gdm. startx does not work as well. So how do I do the oposite of this?

By: Andrew

Andrew — Wed, 20 Jul 2011 03:25:46 +0000

+1 to Thomas suggestion.

You MUST chmod 600 /swapfile1. Otherwise your box will get owned!

http://www.juniper.net/security/auto/vulnerabilities/vuln2678.html

By: Vlad

Vlad — Wed, 29 Jun 2011 15:19:08 +0000

great post!

By: Thomas

Thomas — Mon, 03 May 2010 09:27:10 +0000

Great howto!

After creating the swap file its permissions should be set so that only root can access the file:

chmod 600 /swapfile1

By: luckyrams

luckyrams — Wed, 03 Mar 2010 14:08:48 +0000

Thanks! I’m newbie to Linux, It helped me in time.

By: Primoz

Primoz — Tue, 12 Jan 2010 18:37:21 +0000

Hi!
First I must say thanks for a great how to.
And secondly, I’m referencing it in Arch Linux wiki how to create swap file.
Hope you agree with it.
If not please contact me.
Link: http://wiki.archlinux.org/index.php/HOWTO_Create_swap_file

By: Gen2ly

Gen2ly — Sat, 05 Dec 2009 02:39:25 +0000

Set swap priority:

• Swapiness is the priority of input/output for swap. To look the current value:
cat /proc/sys/vm/swappiness

To change the swap priority (lower value means less swapping):
sysctl vm.swappiness=10

To have this value set at boot add it to /etc/sysctl.conf
vm.swappiness=0

By: acidtoi

acidtoi — Tue, 10 Nov 2009 01:12:26 +0000

hi,
i’m about to install ubuntu karmic on a new computer with thre sata hard drives.

I usually allocate a little more of current ram in swap partition (5 gigas) so I can safely hibernate, but on a post I read in FreeBSD forums there’s a link to FreeBSD manual where states there should be a swap partition for every disk, not just one swap for the whole system.

So, I know Linux is not *BSD but I wonder if the same is applicable here because installing a swap of 5 gigs in all three sata seems a waste of space to me!

cheers!

By: Alex

Alex — Fri, 10 Apr 2009 19:45:11 +0000

Thank you for the guide; I’d like to add another detail. In this line one may choose to use other units to make things more simple:

# dd if=/dev/zero of=/swapfile1 bs=1024 count=524288

You can turn it into:

# dd if=/dev/zero of=/swapfile1 bs=1M count=512

This means that the block size is 1 MB, so count=512 means “I need 512 megs”, there is no need to do any other calculations.

By: Mosab

Mosab — Wed, 07 May 2008 18:29:01 +0000

Thanks, I have been looking for the last step for months heh.

By: asdffdsa

asdffdsa — Sat, 20 Oct 2007 08:25:31 +0000

Thanks for the help. But how would I go about deleting this swapfile? Also, how does creating a swapfile this way differ from creating a separate partition for one? I only ask because I would like to have multiple installs of linux on my system, and I would like them to share the same swapfile.

Recently, I’ve been trying to create a swapfile partition and it’s not being recognized, so I’ve been having trouble.

By: some_guy

some_guy — Fri, 01 Jun 2007 02:35:28 +0000

If you don’t want to reboot the machine to enable the new swapfile, after step f) you can issue these commands:

swapoff -a
swapon -a

to first stop and then start all swaps in /etc/fstab

By: nixcraft

nixcraft — Wed, 17 Jan 2007 22:16:50 +0000

anon,

Thanks for heads up!

By: anon

anon — Wed, 17 Jan 2007 22:00:47 +0000

TYPO: vi /etc/fstatb
It should be fstab