Increase virtual memory in virtualmin (ubuntu)

Make an empty file of e.g. 2GB (must be root or use sudo):

# dd if=/dev/zero of=/swapfile bs=1024 count=2097152
OR
# fallocate -l 1G /swapfile

Set it to only be readable by root (because memory can contain anything, including sensitive data):

# chmod 600 /swapfile

Format it for swap usage:

# mkswap /swapfile

Enable it in /etc/fstab (skip this if you already had swap on /swapfile):

# echo ‘/swapfile none swap sw 0 0’ >> /etc/fstab

Turn it on:

# swapon -a

If you already have swap on /swapfile, do the following first:

# swapoff -a
# rm /swapfile