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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.
[root@localhost ~]# free -m total used free shared buff/cache available Mem: 2797 144 2515 8 137 2504 Swap: 2247 0 2247
How to Clear Cache Memory in Linux
Also Read: 10 Useful swapon command examples in Linux (RedHat/CentOS 7/8)
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.
[root@localhost ~]# sync; echo 1 > /proc/sys/vm/drop_caches
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.
#!/bin/sh
sudo sh -c "sync; echo 1 > /proc/sys/vm/drop_caches"
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.
[root@localhost ~]# sync; echo 2 > /proc/sys/vm/drop_caches
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.
#!/bin/sh
sudo sh -c "sync; echo 2 > /proc/sys/vm/drop_caches"
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.
[root@localhost ~]# sync; echo 3 > /proc/sys/vm/drop_caches
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.
#!/bin/sh
sudo sh -c "sync; echo 3 > /proc/sys/vm/drop_caches"
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