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)
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.
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".
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:
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
#/host/ubuntu/disks/swap.disk none swap loop,sw 0 0
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.
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.
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:
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".
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**
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.
a) To the issue of "best-practices", in general, "best-practices" are in the eye of the beholder.
That's why this site is not called "Ask Microsoft Tech-Support", right? :)
b) to the simple issue of disabling swap,
sudo swapoff -v /swap.img
sudo nano /etc/fstab
and commenting # out the /swap.img line (usually at the end of the file)
then cntl-O and cntl-X (lower-case) to write-out the changes and exit nano
works just fine (if you do it right, backing-up the original fstab file before starting your editor before making any changes would be good practice), just as not swapping works fine except when you allow the system to run out of physical memory, etc etc etc. Yes this is all true. But indicates much-bigger problems, and running off a swapfile is still going to be far slower than using RAM (even a flash drive). And quite often if you do run out of physical memory and hit a swapfile, the end-result will be the same: you're going to have to reboot because system performance will drop to near-zero.
A better practice would be to monitor available RAM and use a tool to notify you if it gets below a certain percentage of installed ram. Unless you want to find-out the above the hard way.
"even-better practice" would be to spawn another thread about that topic...
c) Google AI referred to this site and gave similar info but got the details wrong. At least the 2nd time I've seen that happen. The details on this page are correct.
thanks
