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I have some sensitive data in RAM that I prefer not to be on disk. How do I disable swap?

I have more than enough RAM. If RAM consumption gets too high I have no problems with processes being terminated. How do I disable swap?

Note: I do not have a swap partition and this is running in a VM (VMware)

Peter Mortensen
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    Even if you have a lot of RAM, it's not the best idea to completely work without swap (see for instance http://www.alexonlinux.com/swap-vs-no-swap ). Depending on your requirements you might consider putting the swap partition on a dm-crypt secured device, so that everything written to it will be encrypted. You have to make sure in such a case, that swap is enabled after encrypted volumes get available, and disabled before the device mapping is disabled, of course (I think that's default on Ubuntu, but I'm not sure). Just search the web for "encrypted swap" to find numerous guides. – soulsource May 13 '14 at 09:01
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    Apropos: http://askubuntu.com/questions/248158/how-do-i-setup-an-encrypted-swap-file You don't need swap until you need it. And then you really need it. –  Oct 28 '15 at 19:19
  • What about a cryptswap ? /dev/mapper/cryptswap1 –  Feb 10 '16 at 04:20
  • similar question on serverfault: https://serverfault.com/q/684771 – drammock Apr 20 '20 at 20:35

8 Answers8

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Using 

sudo swapoff -a

is the usual way to turn off swap, with the swapon -a command used to turn it back on. See man swapoff for more information about turning off swap for explicit devices.

cshubhamrao
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ubfan1
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You may disable swap after reboot by just commenting out (add # in front of the line) the swap entry in the /etc/fstab file. It will prevent the swap partition from automatically mounting after a reboot. To do this in a single command:

sudo sed -i '/ swap / s/^\(.*\)$/#\1/g' /etc/fstab

Or simply:

sudo sed -i '/ swap / s/^/#/' /etc/fstab

Now your swap entry on /etc/fstab will look similar to this:

#UUID=xxxxxxxx-xxxx-xxxxx-xxx-xxxxxxxxxxx none            swap    sw              0       0

With your own specific numbers and lower case letters instead of the letters "x".

Peter Mortensen
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Avinash Raj
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    Why does your quoted UUID have some concrete digits? Should they be identical for all UUIDs? My partitions' UUIDs don't have any coincidence with your specified digits. – Ruslan May 31 '16 at 17:51
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    Your sed commands don't work in case the fields are separated by tabs (not spaces). It is better written as sed -ri '/\sswap\s/s/^#?/#/' /etc/fstab PS: I also added #? to prevent additional changes to /etc/fstab when the line is already disabled. – Alek_A May 11 '18 at 21:34
  • How does this address sensitive data that may already exist on disk due to previously enabled swap? I think this is the OPs main concern based on the question. See my answer here. – Elder Geek Dec 14 '19 at 18:51
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    I like this the best. – Vasantha Ganesh Apr 02 '21 at 05:06
  • doesnt work for me (Ubuntu 20.04), the line is still uncommented /swap.img none swap sw – Mayou36 Mar 12 '24 at 18:41
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sudo swapoff -a

Above command disables swap only for a current session, you need to comment out swap partition in /etc/fstab file. To do this you just need to add "#" (comment line) to the beginning of swap line. Steps are as:

  1. Open fstab file, type sudo gedit /etc/fstab in terminal.

File's contents would look like this:

proc            /proc           proc    nodev,noexec,nosuid 0       0
/host/ubuntu/disks/root.disk /               ext4    loop,errors=remount-ro 0       1
/host/ubuntu/disks/swap.disk none            swap    loop,sw         0       0
#/dev/sda10 /media/ASD  vfat    defaults    0   0
#/dev/sda1  /media/98   vfat    defaults    0   0
  1. Just add hash (#) to the beginning of the swap partition line, so the line looks as:

#/host/ubuntu/disks/swap.disk none swap loop,sw 0 0

  1. Reboot your PC
Sohail xIN3N
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11

It may be lame solution, but I used it often. You can simply type

sudo -s
crontab -e

And add

@reboot sudo swapoff -a

So, it will be disabled automatically on boot.

pl_rock
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Andrew Zhilin
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    I hope it goes without saying that this is a very poor method. Why create a boot-time task to turn off another option, when there's another file that can be edited to stop it being turned on in the first place – underscore_d Oct 29 '15 at 18:18
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    Perhaps not as aesthetically pleasing, but there's nothing poor about it. If you're already very used to using crontab then this solution will roll of the fingers a bit easier and make more sense than simply blindly copying what other user on S.E. told you to do to /etc/fstab. And, you'll still remember how to do it to a new computer without having to run to google again. I happen to barely even know what crontab is and am much more familiar with disk partitions anyway but the logic still stands. – Nicholas Pipitone Aug 03 '19 at 05:26
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    Actually, this might be the better solution. Because /etc/fstab suggestions only work for swap partitions. This solution applies to linux setups regardless of whether or not they use a partition or a swapfile. – Nicholas Pipitone Aug 03 '19 at 05:30
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    @NicholasPipitone /etc/fstab solutions also work for swap files which are also mounted in /etc/fstab. See my answer here. – Elder Geek Dec 14 '19 at 18:44
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    None of the fstab options listed worked for me. This option suffices until I discover what is keeping swap "alive" on my system. – James Mar 25 '23 at 13:25
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If you're concerned about the content of the swap, you can always turn it off as specified in the usual way with sudo swapoff -a and then fill the swap device with zeros or random data using dd.

First use the content of fstab to find your swapfile or device (less /etc/fstab).

Having located it and double and triple checked its location at say sda5 or /swapfile (swap partitions were replaced by default with a swapfile in Ubuntu 17.04 (Zesty Zapus) and beyond).

In the case of a swap partition or drive (prefaced with /dev): issue the "disk destroyer" command (not to be used lightly),

sudo dd if=/dev/zero of=swap, replacing the word swap with the swap device or file you located in /etc/fstab

to blast it full of zeros or

sudo dd if=/dev/random of=swap again replacing the word swap with the swap device or file you located in /etc/fstab

to blast it full of random data.

In the case of a swapfile (prefaced with only a path):, you can simply delete the file with sudo rm /path/to/swapfile, but it's better to just fill it with garbage as described above, so that the next time you turn swap on with

swapon -a

the system will happily use it again. If you have plenty of RAM you may not need swap at all. Issue the command

free

when the system is under heavy load and see how much is in use to make this determination.

If you determine that you permanently don't need swap (for hibernation or anything else) you can simply comment out that line in fstab as suggested here.

free

Peter Mortensen
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Elder Geek
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2

Go into a terminal and execute this command: gnome-disks. It is not installed in all distributions. If so, follow the instructions printed to install it and try again. Look for a device with the word 'swap' on the left pane. It usually has a size the same as your physical memory. Click the square button to disable it. Authenticate this change with your root password.

Screenshot:

Enter image description here

In the System Monitor application (gnome-system-monitor), you will see it reports the swap area as 'not available'. The swap area is disabled, but not deleted. You can enable it easily again in the future. Deleting the swap space has caused my system no harm, but you will create more work for yourself if you do decide you want it back (hibernation) in the future.

To prevent it from mounting at startup, you should go into the "Edit Mount Options..." in gnome-disks and uncheck "Mount at startup".

Peter Mortensen
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user170544
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    Do you think that this answers the users concern about having sensitive data on the swap partition? Can you tell us why? – Elder Geek May 09 '14 at 02:33
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    The user's main point was asking how to disable swap. If you have sensitive data, you should be using pre-boot encryption ideally. – user170544 May 09 '14 at 03:28
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    I respectfully disagree. When I read the question the first sentence I come across is "I have some sensitive data in ram that i prefer not to be on disk." I believe this was his main concern which is why he started with it. Regardless, I believe I have covered every aspect of his question in my answer. Consider it a helpful example. – Elder Geek May 09 '14 at 11:11
1

Replace the defaults with sw,noauto in the line which consists of the swap entry in the file /etc/fstab:

/dev/mapper/centos-swap swap  swap    sw,noauto        0 0

(The path /dev/mapper/centos-swap is probably different for you).

Now checkout the output after reboot, your swap never get mounted:

$ free -m
              total        used        free      shared  buff/cache   available
Mem:           3791         100        3408           8         282        3483
**Swap:             0           0           0**
Carolus
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askb
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0

Disable Swap

Run the following command to disable Swap:

sudo swapoff -a

Now remove the Swap file:

sudo rm /swap.img

It is safe and does not require a reboot.

R1W
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