Adding a swap file to small Digital Ocean droplets on Ubuntu
If you have a smaller droplet on DigitalOcean, chances are you will need to create a swap file at some point. A good example of needing a swap file is if you get the following error in your daily cron:
/etc/cron.daily/apt: FATAL -> Failed to fork.
The error above normally occurs when you run out of RAM needed to run the cron job.
Just how much free RAM do you have? This is easy to check with
# free -mh
total used free shared buffers cached
Mem: 490M 403M 86M 360K 17M 254M
-/+ buffers/cache: 131M 358M
Swap: 0B 0B 0B
A typical rule of thumb for creating a swap file is that you want a swapfile that is twice the amount of RAM you have. In our case, we are on a 500MB RAM droplet, so we will want to create a 1GB swap file. Before we create the file, let's ensure we have enough space on our drive:
# df -h Filesystem Size Used Avail Use% Mounted on udev 235M 4.0K 235M 1% /dev tmpfs 50M 404K 49M 1% /run /dev/disk/by-label/DOROOT 20G 8.4G 11G 46% / none 4.0K 0 4.0K 0% /sys/fs/cgroup none 5.0M 0 5.0M 0% /run/lock none 246M 0 246M 0% /run/shm none 100M 0 100M 0% /run/user
In our case we have 8.4GB available, which is enough to create a 1GB swap file. So let's get started. For the purposes of this tutorial, we'll put the swap file in the root of the drive and call it 'swapfile'. We'll use fallocate which preallocates space to a file. The -l option specifies the length of the allocation (size of file) in bytes. You may us M or G to specify MB or GB:
# sudo fallocate -l 1G /swapfile # sudo chmod 600 /swapfile # ls -la /swapfile -rw------- 1 root root 1048576000 May 30 09:17 /swapfile
Next, we will convert the regular file into a file that can be used as a swap file, and then enable the swap file:
# sudo mkswap /swapfile # sudo swapon /swapfile # sudo swapon -s Filename Type Size Used Priority /swapfile file 1023996 0 -1
If you run free -mh now you will see that the swapfile has been created and enable and is now ready for use:
# free -mh
total used free shared buffers cached
Mem: 490M 331M 158M 5.8M 21M 141M
-/+ buffers/cache: 169M 320M
Swap: 999M 0B 999M
The only thing left to do is add an entry to fstab to ensure the swap file persists between reboots:
echo "/swapfile none swap sw 0 0" | sudo tee /etc/fstab -a
You should be set now!