Extend ubuntu swap without reboot and risk

zhang

6/3/24, 2:08 PM

I manage an Ubuntu server part-time in a scientific research laboratory, which has 512G memory and 8G swap space. Recently, we occasionally encounter low-frequency memory shortage, so I plan to expand the swap space. Currently, this server cannot accept any shutdown or accident. I find that they all recommend restarting the device after configuring the swap,

eg: Increase swap in 20.04

and I'm not sure if I can avoid this

My plan is:

First, find current swap file

$ sudo swapon --show
NAME      TYPE SIZE USED PRIO
/swap.img file   8G 7.3G   -2

swap off and remove

sudo swapoff /swap.img 
sudo rm /swap.img

create new swap file

sudo dd if=/dev/zero of=/swap.img bs=1M count=92160

sudo chmod 600 /swap.img

create swap

sudo mkswap /swap.img

enable swap

sudo swapon /swap.img
# not reboot

Is it ok and safe to do?

0 + 5

server

swap

Marco

6/3/24, 2:24 PM

No need to remove "old" swapfile, create an **additional** one (not overwriting!). Linux can work with multiple swapfiles. https://askubuntu.com/questions/563430/how-to-create-a-swapfile

zhang

6/3/24, 2:47 PM

Hi, thanks for your help, sorry for more question, I am not sure is it necessary to add the new swapfiles to `/etc/fastb` for if I just add not instead the old swap, or the `swapon` will do it automatic

Marco

6/3/24, 2:57 PM

If you want to have the config over a reboot, you need to add it in `/etc/fstab`.

popey

6/3/24, 3:33 PM

(however, yes, you can create a second swap file (I do this all the time on servers) and just enable it for that session, without modifying `/etc/fstab`) (to complete the answer)

waltinator

6/3/24, 4:48 PM

Creating a swap file with `dd` will create a discontinuous file, which won't work for swap. Read `man mkswap swapon fstab`.

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