Your cache will be freed up as soon as a process needs memory. It is designed to use all available memory. Under Linux it is completely OK to run with no 'free' memory (the one free refers to as 'free') as long as you have enough available (or total -buffers/cache is enough). Clean up APT cache in Ubuntu. Ubuntu uses APT (Advanced Package Tool) for installing, removing and managing software on the system, and in doing so it keeps a cache of previously downloaded and installed packages even after they’ve been uninstalled. The APT package management system keeps a cache of DEB packages in /var/cache/apt/archives.

The linux file system cache (Page Cache) is used to make IO operations faster. Under certain circumstances an administrator or developer might want to manually clear the cache. In this article we will explain how the Linux File System cache works. Then we will demonstrate how to monitor the cache usage and how to clear the cache. We will do some simple performance experiments to verify the cache is working as expected and that the cache flush and clear procedure is also working as expected.

How Linux File System Cache Works

The kernel reserves a certain amount of system memory for caching the file system disk accesses in order to make overall performance faster. The cache in linux is called the Page Cache. The size of the page cache is configurable with generous defaults enabled to cache large amounts of disk blocks. The max size of the cache and the policies of when to evict data from the cache are adjustable with kernel parameters. The linux cache approach is called a write-back cache. This means if data is written to disk it is written to memory into the cache and marked as dirty in the cache until it is synchronized to disk. The kernel maintains internal data structures to optimize which data to evict from cache when more space is needed in the cache.

During Linux read system calls, the kernel will check if the data requested is stored in blocks of data in the cache, that would be a successful cache hit and the data will be returned from the cache without doing any IO to the disk system. For a cache miss the data will be fetched from IO system and the cache updated based on the caching policies as this same data is likely to be requested again.

When certain thresholds of memory usage are reached background tasks will start writing dirty data to disk to ensure it is clearing the memory cache. These can have an impact on performance of memory and CPU intensive applications and require tuning by administrators and or developers.

Using Free command to view Cache Usage

We can use the free command from the command line in order to analyze the system memory and the amount of memory allocated to caching. See command below:

Clear Pip Cache Ubuntu

What we see from the free command above is that there is 7.5 GB of RAM on this system. Of this only 209 MB is used and 6.5 MB is free. 667 MB is used in the buffer cache. Now let’s try to increase that number by running a command to generate a file of 1 Gigabyte and reading the file. The command below will generate approximately 100MB of random data and then append 10 copies of the file together into one large_file.

Now we will make sure to read this 1 Gig file and then check the free command again:

We can see the buffer cache usage has gone up from 667 to 1735 Megabytes a roughly 1 Gigabyte increase in the usage of the buffer cache.

Proc Sys VM Drop Caches Command

The linux kernel provides an interface to drop the cache let’s try out these commands and see the impact on the free setting.

We can see above that the majority of the buffer cache allocation was freed with this command.

Experimental Verification that Drop Caches Works

Can we do a performance validation of using the cache to read the file? Let’s read the file and write it back to /dev/null in order to test how long it takes to read the file from disk. We will time it with the time command. We do this command immediately after clearing the cache with the commands above.

It took 8.4 seconds to read the file. Let’s read it again now that the file should be in the filesystem cache and see how long it takes now.

Boom! It took only .2 seconds compared to 8.4 seconds to read it when the file was not cached. To verify let’s repeat this again by first clearing the cache and then reading the file 2 times.

It worked perfectly as expected. 8.5 seconds for the non-cached read and .2 seconds for the cached read.

Conclusion

The page cache is automatically enabled on Linux systems and will transparently make IO faster by storing recently used data in the cache. If you want to manually clear the cache that can be done easily by sending an echo command to the /proc filesystem indicating to the kernel to drop the cache and free the memory used for the cache. The instructions for running the command were shown above in this article and the experimental validation of the cache behavior before and after flushing were also shown.

How To Clear Ram Cache In Ubuntu Computer

More Linux resources

Swap memory is usually a 'set it and forget it' type of affair. Drivers victor sound cards & media devices. Most enterprise environments have swap built into the systems, and these memory caches are not manipulated unless there is an apparent lack of memory available or if a server crashes due to the OOM killer (out of memory) error. However, there is a niche situation that can cause an administrator to need to clear the system swap manually. If that is the situation that you find yourself in, you’ve come to the right place. This article is a discussion about this situation and the solution required.

Feeling Swappy?

Occasionally, a system uses a high percentage of swap memory even when there is RAM available for use. The culprit here is the ‘swappiness’ of the system. Yep, you read that right..swappiness. So now that you know the lingo, you're ready to explore what it means. Swappiness refers to the kernel parameter responsible for how much and how often that the system moves data from RAM to swap memory.

Clear Dns Cache Ubuntu

The default value for swappiness is 60; however, you can manually set it anywhere between 0-100. Small values cause little swapping to occur, whereas high values can cause very aggressive swapping. A value of zero causes no swapping at all to occur, so if you want to minimize swapping to its lowest possible value without turning it off, you should set it to at least one.

How To Clear Ram Cache In Ubuntu 20.04

[ Free download: Advanced Linux commands cheat sheet. ]

If you wanted to change up the swappiness of your system, the procedure is very straight-forward. You can check your current swappiness setting by running the following command:

How To Clear Ram Cache In Ubuntu

It should look something like this: