How to flush cache in Linux

Hello guys,

Me again with a very interesting problem. Today I was working on some tasks as usual and I discovered that something is wrong with one of our systems and the vehicles are not updated actively. Something went wrong with the MQTT connection and that’s how I arrived to write How I found a simple UI Viewer for InfluxDB article.

While I debugged the problem I observed that the server’s RAM memory is full, but guess what, the memory used was 489640 and free memory 359256 from a total of 4GB. That’s why I came with the great idea As you can see below, the buff/cache memory is above 3GB (3189056).

$ top

top - 13:42:55 up 168 days, 5:26, 1 user, load average: 0.00, 0.00, 0.00
Tasks: 109 total, 1 running, 67 sleeping, 0 stopped, 0 zombie
%Cpu(s): 0.3 us, 0.0 sy, 0.0 ni, 99.5 id, 0.0 wa, 0.0 hi, 0.0 si, 0.2 st
KiB Mem : 4037952 total, 359256 free, 489640 used, 3189056 buff/cache
KiB Swap: 0 total, 0 free, 0 used. 3268392 avail Mem 

Check the cache memory

$ free -m

              total used free shared buff/cache available
Mem: 3943 503 365 1 3074 3167
Swap: 0 0 0

Clear the cache memory

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

Now you can check again the cache, and surprise

$ free -m

              total used free shared buff/cache available
Mem: 3943 505 3123 1 314 3206

And this is how it looks now my result of top command

$ top

top - 13:46:19 up 168 days, 5:29, 1 user, load average: 0.00, 0.00, 0.00
Tasks: 110 total, 1 running, 67 sleeping, 0 stopped, 0 zombie
%Cpu(s): 0.0 us, 0.2 sy, 0.0 ni, 99.8 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
KiB Mem : 4037952 total, 3196540 free, 517812 used, 323600 buff/cache
KiB Swap: 0 total, 0 free, 0 used. 3282840 avail Mem 

Automate this with a cronjob

I know that you’re lazy, so do I. Now let’s go back in business and create a Cronjob that automates this process for you.

$ crontab -e

A new text editor will open now, probably it’s VIM. All you have to do is to add at the end of file the following:

# m h dom mon dow command

0 2 * * * sync; echo 3 | sudo tee /proc/sys/vm/drop_caches

This cron will execute every day at 2am.

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