Ubuntu – a “Swap Area”

partitioningswapsystem-installation

So I noticed this question has not been asked directly;

What is this "Swap Area" people keep referring to when it comes to installing Ubuntu?

Best Answer

Summary

The Swap Area is just fake RAM that lives on your hard drive. It is much slower than actual RAM, but is necessary in many cases to keep a computer running normally. A good rule of thumb is to have as much swap space as you do normal RAM.

Memory

Your computer has a couple different kinds of memory that we need to talk about. Your files and operating system are stored on your hard drive (commonly HDD). This is relatively slow and cheap, but is persistent between system shutdowns. Your computer also has RAM (Random Access Memory) which is much faster, more expensive, and loses its contents when your computer loses power. In order to run a program, it is first copied from your HDD to your RAM (which is much faster) so that it can execute in close to real time.

Swap

However, we should ask the question: what happens if you run out of RAM but want to open another program? The answer isn't good; your computer freezes until there is enough RAM to complete the operation (this is commonly called "thrashing"). Although you might only have a few Gigabytes of RAM, most computers have more HDD space than they know what to do with. So we can use some of that extra space as fake "RAM" in a pinch. That is what swap space is; emergency RAM that lives on your hard drive.

Now that we have some swap space on our hard drive, running out of RAM isn't as big of a deal. Now when we run out and wish to open another program, the operating system looks through all of the open programs currently in RAM, and chooses one that hasn't been used for a while. It then copies that program out of RAM and stores it in swap space, freeing up room for the new program. If in the future we want to access the "swapped out" program, the operating system simply copies it back to RAM, potentially swapping out other programs in the process.

Partition vs. File

When creating a swap space, you have two choices. You can make a separate partition on your hard drive, which is recommended in Ubuntu and necessary if you wish to hibernate your system. Or, you can create a Swap File (called the Pagefile in Windows) on your hard drive. Technically a swap partition will out-perform a swap file, but the difference will likely be negligible. Also note that if you have multiple linux distributions on the same hard drive, they can share a single swap partition (swap partitions do not have a file system).

Guidelines

If you are installing Ubuntu for the first time, you might as well make a swap partition. This is the default in the Ubuntu installer, and also my personal recommendation. On the other hand, if you do not have any swap space and would like to add some after installation, it may be much easier and faster to use a swap file.

In terms of size, if you have no idea how big to make it, a good baseline (and the default in the Ubuntu installer) is to have the same amount of swap as you do RAM. That being said, this is only a very general guideline, and depends on how you use your system. There is nothing wrong with having no swap space. If you start running out of RAM, just make your swap space larger.

sudo fallocate -l 4G /swapfile  # Create a 'swap-file'; 4G in this case
sudo chmod 600 /swapfile        # Set the necessary file permissions
ls -lh /swapfile                # Check
sudo mkswap /swapfile           # Mark the file as 'swap'
sudo swapon /swapfile           # Enable the 'swap'
sudo swapon --show              # Check
free -h                         # Another check

Edit /etc/fstab and make the changes permanent. Use these commands to do the changes:

sudo sed 's/^.*swap.*$//' /etc/fstab -i.bak                # Remove the previous swap entries 
                                                           # and create a backup copy of the file
echo '/swapfile none swap sw 0 0' | sudo tee -a /etc/fstab # Add a new entry

Or edit /etc/fstab and add the the following entry manually:

/swapfile none swap sw 0 0

That is it.

Ideas for additional tweaks (I would prefer to use the default settings for normal swap usage):

Change the frequency of RAM to SWAP data copy:

sudo sysctl vm.swappiness=10    # value 0-100: low value low frequency
cat /proc/sys/vm/swappiness     # Check

Change the frequency of Cache flush:

sudo sysctl vm.vfs_cache_pressure=50 # 0-100: high value high frequency
cat /proc/sys/vm/vfs_cache_pressure  # Check

Make the above changes permanent:

sudo cp /etc/sysctl.conf{,.bak} # Create a backup copy of the file '/etc/sysctl.conf'
echo -e '\nCustom settings: value 0-100; default 100\nvm.swappiness=10\nvm.vfs_cache_pressure=50' | sudo tee -a /etc/sysctl.conf

Or edit /etc/sysctl.conf and add the the following entries manually:

# Custom settings: value 0-100; default 100
vm.swappiness=10
vm.vfs_cache_pressure=50

Ubuntu – a “Swap Area”

Best Answer

Summary

Memory

Swap

Partition vs. File

Guidelines

See also

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Best Answer

Summary

Memory

Swap

Partition vs. File

Guidelines

See also

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