How to Clear Cached Memory in Linux

In the world of Linux, efficient system performance is a key objective for administrators and users alike. A critical aspect of maintaining this performance is managing the system’s cached memory and buffer cache. These components are designed to store frequently accessed data and instructions, reducing the time it takes to access them from disk. However, over time, the cache can accumulate data that is no longer needed, potentially leading to reduced system efficiency and performance issues.

This guide provides instructions on how to clear the RAM memory cache on Linux/Unix systems using command-line methods.

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How to Clear RAM Cache in Linux

Linux offers three methods for purging memory cache, allowing you to optimize system performance according to your specific needs.

• For a comprehensive clearance of PageCache, dentries, and inodes from the cache memory, essentially purging all cached data, use the following command:

  
  sync; echo 3 | sudo tee /proc/sys/vm/drop_caches
  
  

• If your goal is to remove only dentries and inodes from the cache memory, execute this command:

  
  sync; echo 2 | sudo tee /proc/sys/vm/drop_caches
  
  

• And, to specifically target and clear the page cache within the cache memory, apply this command:

  
  sync; echo 1 | sudo tee /proc/sys/vm/drop_caches
  
  

The `sync` command precedes each of these operations to ensure that all files currently held in the cache are first synchronized with the storage disk. The following command, indicated by the “;`, is then executed to clear the designated areas of cache memory as requested.

Automating Cache Clearance with Crontab

For periodic cache clearance, you can schedule a cron job. Use the following steps to set up an automatic cache flushing schedule:

1. Open a terminal and run `crontab -e` to edit the crontab.
2. Add the following entry to schedule the cache clearance:

   
   10 * * * * sync; echo 3 | sudo tee /proc/sys/vm/drop_caches
   
   

   This cron job runs hourly, clearing the memory cache on your system.

However, on production servers, scheduling a cache clearance is generally not recommended as it may lead to data corruption or loss. Exercise caution before running such commands in a production environment.

Checking Cached Memory in Linux

To determine the amount of cache memory used by a Linux system, use the free command. The output, displayed in megabytes (MB), shows the cached memory usage. For example:

free -m 

This command will display the total, used, free, shared, buffer, and cached memory, with the last column indicating the amount of cached memory.

             total       used       free     shared    buffers     cached
Mem:         16050      15908        142          0        120      12953
-/+ buffers/cache:        834      15216
Swap:            0          0          0

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

Conclusion

In conclusion, managing the memory cache in Linux is an essential task for optimizing system performance. While the cache plays a crucial role in speeding up data access, an overloaded cache can slow down the system. The methods outlined in this article provide straightforward ways to clear different types of cache, including PageCache, dentries, and inodes, ensuring that your Linux system runs efficiently. Additionally, the option to automate this process through cron jobs offers convenience, but it should be approached with caution, especially on production servers, to avoid potential data loss or corruption.

Finally, understanding how to monitor cache usage with the free command is a valuable skill for any Linux administrator or user, helping in making informed decisions about memory management. By regularly monitoring and managing the memory cache, you can maintain the optimal performance of your Linux