Clearing memory in linux

How to Clear RAM Memory Cache, Buffer and Swap Space on Linux

In this article, we will see How to Clear RAM Memory Cache, Buffer, and Swap Space on Linux. In every system we do come across caches that have unwanted files and can harm our system, the same thing happens in Linux cache and if you want to clear the cache and free some memory then Linux has many commands to do that.

To Clear Cache in Linux:

In all the Linux systems we have three options to clear cache without interrupting any services or processes.

Example 1: To Clear PageCache only

Syntax :

The command # free -h will give us the status of the memory

drop_caches is used a clean cache without killing any application, you can run the # free -h command to see the difference between used and free memory before and after clearing the cache

Example 2: To Clear dentries and inodes

Syntax:

Example 3: To Clear PageCache, dentries and inodes

Syntax:

Now using Linux Kernel, to free Buffer and Cache in Linux we will Create a shell script to auto clear RAM cache daily, through a cron scheduler task., the command vim script.sh is used to create a shell script “script.sh”

Now in script, you have to add the below syntax:

Now to set run permission, to clear ram cache, you have to call the script whenever required, setting a cron to clear RAM caches every day for 3 hours.

Example 4: To Clear Swap Space in Linux

You can clear the swap space by running the below command

Syntax :

You can run the # free -h command to see the difference between used and free memory before and after clearing the swap space

Add the above command to a cron script, Here we are going to combine this two different command into one single command, to form a proper script which will help us to clear Swap Space and RAM Cache.

echo 3 > /proc/sys/vm/drop_caches & & swapoff -a & & swapon -a & & printf ‘\n%s\n’ ‘ ‘ Ram-cache and the swap get cleared’

Now Ram cache and swap will be cleared you can run # free -h command to see

After running the command you will get output like this

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How to clear swap memory in Linux

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Swap memory is usually a «set it and forget it» type of affair. 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.

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.

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.

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:

It should look something like this:

Now, you can see that my system has a swappiness value of 30. To alter the value, you want to use the following:

To verify the value that you set, simply cat the swappiness file that you looked at earlier to find out the original value. Easy day. Now that you understand the underlying parameters that control the swap behavior on our system, you’re ready to learn how to clear that memory, should the situation arise. For the first time in your terminal life, things are going to be easy here.

To clear the swap memory on your system, you simply need to cycle off the swap. This moves all data from swap memory back into RAM. It also means that you need to be sure you have the RAM to support this operation. An easy way to do this is to run ‘free -m’ to see what is being used in swap and in RAM. Once you power it off, you can wait an arbitrary amount of time (30 sec or so) to give the operation time to complete, then power the swap back on. This clears the swap memory cache and re-enables it. Here are all of the commands you’ll need!

Hopefully, this quick tip helps you clear your system swap memory if you ever find yourself in need of just such a fix.

For more information on swap space see my article outlining the basics here.

Want to try out Red Hat Enterprise Linux? Download it now for free.

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How to Clear Memory Cache in Linux

Sometimes the system goes out of memory due to huge RAM is used by cached objects. In that cases, either you need to increase physical memory in the system or add more swap space. You can also instruct kernel to clear RAM memory cache on system by adding a number in /proc/sys/vm/drop_caches file.

It is safe but not recommended to clear the memory cache on a Linux system. Clearing the Memory cache in Linux systems slows down the system performance as reading files from memory is much faster than persistent disk. Since it discards cached objects from memory, it may cost a significant amount of I/O and CPU to recreate the dropped objects. This tutorial will help you to clear the memory cache on Linux/Unix system via the command line.

How to Clear Memory Cache on Linux

There are three options available to clear the memory cache in Linux. Choose one of the below options to flush the Linux system cache memory as per your requirements.

• Clear PageCache, dentries and inodes in cache memory. In short it will clear all the memory cache:
• Clear dentries and inodes only in cache memory
• Clear page cache only in cache memory

Here the first command sync is used to synchronize all the in-memory cache files to the persistent storage. The next command is separated with a “;”. Once the first command is completed, the next command will be triggered to clear cache memory.

Scheduleng the Clear Memory Cache with Crontab

You can also schedule a corn job to clear the cache on a regular basis. Schedule the following in system crontab to automatically flush cache memory at a regular interval.

Open a terminal and execute ‘crontab -e’ command to edit crontab:

Append below entry to the file:

The above cron will execute on every hour and flushes the memory cache on your system.

On the production servers, it is not recommended to schedule a clear cache command. It can lead to data corruption or data loss. So beware before running the above command in a production environment.

How to find Cached Memory in Linux

Use free command to find out cache memory uses by Linux system. The output of the free command is like below

Here the last column is showing cached memory (12953 MB) on Linux system. The -m option is used to show output MB’s.

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How to Clear Swap Memory in Linux

Swap is a virtual memory concept that allows your system to use a portion of your hard drive as the physical memory (RAM). Your system swaps the inactive pages in memory in RAM to this swap space on the hard disk. This way, your system has more free RAM available for other programs.

I have shown you to check RAM in Linux and I have also discussed how to check swap usage on Linux. In this quick tip, I’ll show you how to clear swap memory in Linux.

Clear swap in Linux

But first, why would you want to clear swap at all? There could be various reasons. Some time your system will use a lot of swap even when plenty of RAM is available.

This may or may not be associated with swappiness of your system. Sometimes it happens that the RAM doesn’t swap back the pages from swap space to RAM. In such cases, you’ll have to manually clear the swap.

Attention

Before clearing the swap, check that you have enough free RAM available to take all the pages from swap. In other words, you should have more free RAM available than the current swap in use.

You can see the state of RAM and swap using the free command in Linux:

Once you are sure that the size of free RAM is bigger than the swap memory in use, you can clear the swap memory by turning it off and on again.

Pun aside, that’s the way to do it. Disable all the swap using this command:

Now turn the swap back on:

That’s it. This simple exercise will clear the swap in your Linux system. I hope you find this little tip helpful. Any questions or suggestions are always welcome.

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How to Drop/Flush/Clear Cache Memory or RAM in Linux (RedHat/CentOS 7/8) in 6 Best Steps

Table of Contents

In this article, I will take you through different steps to drop/flush/clear cache memory in Linux. As you might be aware Linux has very robust Memory Management System but still if you need to clear cache memory due to certain reasons then you need to do it manually.

Someday if you ran into a problem where you find that updated data is not visible or accessible from Page Cache then you might need to clear cache memory once and check if it helps. This is required because once the cache memory is cleared then System has to access the files from Disk and hence you will get the updated data. The only downside is that clearing Cache memory will slow down your systems atleast until the cache re-build takes place.

What is Cache

Cache are usually a small reserve amount of memory used generally for faster access of disk files and directories. This Cache is generally called as Page Cache in Linux.

How Page Cache Works in Linux

Page cache is the main Linux disk Cache used in Linux. System will usually add a page based on User read process request. If the requested page is not available in the Cache then the page will be added to the disk and will be available as long as it is needed. This increases the performance of Input Output Read Operations. The only criteria is that Cache should be enough memory available. Page Cache also needs to be in sync with the disk files as new changes in the file should be synced with Cached data or it will marked as dirty and eventually will be removed from the Page Cache.

How to Check Linux Cache Memory

You might be aware of free command in Linux command line to check the current memory usage of the System. Using this command, you can check the total memory, used memory, cache or buffer memory, available memory etc as can be observed from below output. As you can see from below output, 137 MB is the current buffer/Cache memory.

How to Clear Cache Memory in Linux

Example 1: How to Clear Page Cache Only

If you want to clear your disk cache then you need to run echo 1 > /proc/sys/vm/drop_caches after running sync command as shown below.

Example 2: How to Clear Page Cache Every day through crontab

You can also set a small script in crontab to clear cache memory every day as shown below. Please note that clearing cache memory everyday might slow down your system. Hence this needs to be carefully setup.

Example 3: How to Clear dentries and inodes Only

If you want to clear your dentries and inodes then you need to run echo 2 > /proc/sys/vm/drop_caches after running sync command as shown below.

Example 4: How to Clear dentries and inodes every day through crontab

You can also set a small script in crontab to clear page cache every day as shown below. Please note that clearing cache memory everyday might slow down your system. Hence this needs to be carefully setup.

Example 5: How to Clear Page Cache, dentries and inodes

If you want to clear your all disk cache, dentries and inodes then you need to run echo 3 > /proc/sys/vm/drop_caches after running sync command as shown below.

Example 6: How to Clear Page Cache, dentries and inodes every day through crontab

You can also set a small script in crontab to clear cache memory every day as shown below. Please note that clearing cache memory everyday might slow down your system. Hence this needs to be carefully setup.

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