How do I allocate memory to work as swap space in an Amazon EC2 instance by using a swap file?
When physical RAM is already in use, Amazon EC2 instances use swap space as a short-term replacement for physical RAM.
Contents of RAM that aren’t in active use or that aren’t needed as urgently as other data or instructions can be temporarily paged to a swap file. This frees up RAM for more immediate use.
The problem is when you don’t have swap space.
Use the dd command to create a swap file on the root file system
Command 1
sudo dd if=/dev/zero of=/swapfile bs=1M count=2048
output
2048+0 records in
2048+0 records out
2147483648 bytes (2.1 GB, 2.0 GiB) copied, 31.5064 s, 68.2 MB/s
Command 2
sudo fallocate –length 2G /swapfile
If the above command is throwing any error (new version of Ubuntu throw error on command –length)
try this sudo fallocate –l 2G /swapfile
Command 3
sudo chmod 600 /swapfile
Command 4
sudo mkswap /swapfile
output
Setting up swapspace version 1, size = 2 GiB (2147479552 bytes)
no label, UUID=e508f3b2-8eaa-4b5a-8bbe-98d150b7da96
Command 5
sudo swapon /swapfile
Enable the swap file at boot time by editing the /etc/fstab file. so that it wont change after restarting the server.
Open the file in the editor:
Command 6
sudo vi /etc/fstab
Add the following newline at the end of the file, save the file, and then exit:
Command 7
/swapfile swap swap defaults 0 0
# To add swap space in centos 6
Basically, we are going to create 1GB file that will consist of zeros only and use that as a swap later.
# dd if=/dev/zero of=/swapfile bs=1M count=1024
Next, we need to set up file so it is can be used as swap space. We will use mkswap command for that:
# mkswap /swapfile
The swap file must be owned by root and have proper permissions:
#chown root:root /swapfile
#chmod 0600 /swapfile
Once this is done, the only thing left is to activate and start using the swap space.
# swapon /swapfile
