How to expand existing swap file?

Question

I'm running Kubuntu 17.10, upgraded from 17.04 in-place.

I have a 2GB swap file on my SSD that was created by the installer when I first installed 17.04. Here's the contents of /proc/swaps (fresh after a reboot from running out of memory):

Filename                                Type            Size    Used    Priority
/swapfile                               file            2097148 0       -1

How can I expand this swapfile to 4GB? I've found plenty of answers about resizing swap partitions and adding new swap files, but nothing about resizing existing ones.

Solution

Resizing the file is the same process as making a swap file. So, you have three options:

1. Add another swapfile. 2 files of 2GB is the same as one of 4GB (ie 4GB swap)
2. Delete this file. and make a new one that is 4GB
3. Reuse this file.

To make new or reuse your current file, you have to type:

sudo swapoff -a   # turn off all swap
sudo rm /swapfile # this step is if you want to delete the current file
sudo dd if=/dev/zero of=/swapfile bs=1M count=4096 #makes a 4GB file
sudo chmod 600 /swapfile #set permission to root only if you made a new file
sudo mkswap /swapfile #converts file to swap format
sudo swapon /swapfile #enable swap on the file.

Note: if you are also using a swap partition it will have to be enabled also.

If you just want to add another 2GB file then:

sudo dd if=/dev/zero of=/swapfile2 bs=1M count=2048 #makes a 2GB file
sudo chmod 600 /swapfile2 #set permission to root only
sudo mkswap /swapfile2 #converts file to swap format
sudo swapon /swapfile2 #enable swap on the file.

Then edit /etc/fstab. Duplicate the entry for your current swapfile, and change the filename to the new file (swapfile2).

Comments

[PerlDuck]

Look at help.ubuntu.com/community/SwapFaq#How_do_I_add_a_swap_file.3‌​F Basically it's disable swap – delete /swapfile – recreate /swapfile of desired size – re-enable swap.

[PerlDuck]

I think in the second case (two files) you also need to add a line to /etc/fstab.

[ravery]

@PerlDuck -- yes, I think you are right.

[PerlDuck]

Actually I didn't know we can have more than one swapfile or -partition.

[ravery]

@PerlDuck -- yes, there can be more than one file and/or partition; even a combination of the two. Hibernating requires a partition, unless you do some fancy system settings to make it use a file.

[Linuxios]

Thanks for the answer -- I wonder, is it worth adding the faster alternative of using fallocate from @PerlDuck's link? Also, should the command from the same to set permissions on the swap file also be included?

[Linuxios]

@ravery: When I ran mkswap it actually came back with insecure permissions 0644, 0600 suggested., but it didn't change them itself, I still had to.