Swap Memory
The tiny droplet I have has 512MB RAM, and 20GB on SSD harddisk.
It’s a waste not to create swap memory out of the 20GB SSD!
So, add a few GB of swap memory to your Ubuntu.
Steps:
# Confirm you have no swap
sudo swapon -s
# Allocate 1GB (or more if you wish) in /swapfile
sudo fallocate -l 1G /swapfile
# Make it secure
sudo chmod 600 /swapfile
ls -lh /swapfile
# Activate it
sudo mkswap /swapfile
sudo swapon /swapfile
# Confirm again there’s indeed more memory now
free -m
sudo swapon -s
# Configure fstab to use swap when instance restart
sudo nano /etc/fstab
# Add this line to /etc/fstab, save and exit
/swapfile none swap sw 0 0
# Change swappiness to 10, so that swap is used only when 10% RAM is unused
# The default is too high at 60
echo 10 | sudo tee /proc/sys/vm/swappiness
echo vm.swappiness = 10 | sudo tee -a /etc/sysctl.conf
credit
http://samwize.com/2014/06/10/cannot-restart-mysql-for-digital-ocean-server-low-memory/
https://www.digitalocean.com/community/tutorials/how-to-add-swap-on-ubuntu-14-04