Clearing PageCache, dentries and inodes in Linux

Like any other operating system, GNU/Linux has implemented a memory management efficiently and even more than that. But if any process is eating away your memory and you want to clear it, Linux provides a way to flush or clear ram cache. Use the commands below to clear PageCache, dentries and inodes, or PageCache, dentries and inodes. Keep it mind it isn't a good idea to auto clear RAM cache on production servers. However, if you are troubleshooting an issue with a runaway process or need to ensure all fetching of data comes from disk clearing cache can be very helpful.

To clear PageCache only.

[root@localhost ~]# sync; echo 1 /proc/sys/vm/drop_caches

To clear dentries and inodes.

[root@localhost ~]# sync; echo 2 /proc/sys/vm/drop_caches

Clear PageCache, dentries and inodes.

[root@localhost ~]# sync; echo 3 /proc/sys/vm/drop_caches

Steps to clear cache on a recurring schedule

Step 1: Create a script to clear PageCache, dentries and inodes.

[root@localhost ~]# vi /home/linuxuser/drop_caches.sh

sync; echo 3 > /proc/sys/vm/drop_caches

Step: Edit crontab to run the script every 59 minutes.

[root@localhost ~]# vi /etc/crontab

SHELL=/bin/bash
PATH=/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root

# For details see man 4 crontabs

# Example of job definition:
# .---------------- minute (0 - 59)
# |  .------------- hour (0 - 23)
# |  |  .---------- day of month (1 - 31)
# |  |  |  .------- month (1 - 12) OR jan,feb,mar,apr ...
# |  |  |  |  .---- day of week (0 - 6) (Sunday=0 or 7) OR sun,mon,tue,wed,thu,fri,sat
# |  |  |  |  |
# *  *  *  *  * user-name  command to be executed
  */59  *  *  *  * linuxuser /home/linuxuser/drop_caches.sh

Verify the configuration

Using the tail command we can view the last X lines of the cron log. With the command below I am viewing just the last 14 lines and I can see when the drop_caches.sh is run and when completed. In the example below the script was run at 09:59:01 and again at 10:59:01. This will be repeated every 59 minutes per the crontab configuration.

[root@localhost ~]# tail -14 /var/log/cron

Sep 12 09:59:01 localhost CROND[17716]: (linuxuser) CMD (/home/linuxuser/drop_caches.sh)
Sep 12 10:00:01 localhost CROND[17740]: (linuxuser) CMD (/home/linuxuser/drop_caches.sh)
Sep 12 10:01:01 localhost CROND[17768]: (root) CMD (run-parts /etc/cron.hourly)
Sep 12 10:01:01 localhost run-parts(/etc/cron.hourly)[17768]: starting 0anacron
Sep 12 10:01:01 localhost run-parts(/etc/cron.hourly)[17777]: finished 0anacron
Sep 12 10:01:01 localhost run-parts(/etc/cron.hourly)[17768]: starting 0yum-hourly.cron
Sep 12 10:11:29 localhost run-parts(/etc/cron.hourly)[17923]: finished 0yum-hourly.cron
Sep 12 10:59:01 localhost CROND[18610]: (linuxuser) CMD (/home/linuxuser/drop_caches.sh)
Sep 12 11:00:01 localhost CROND[18630]: (linuxuser) CMD (/home/linuxuser/drop_caches.sh)
Sep 12 11:01:01 localhost CROND[18670]: (root) CMD (run-parts /etc/cron.hourly)
Sep 12 11:01:01 localhost run-parts(/etc/cron.hourly)[18670]: starting 0anacron
Sep 12 11:01:01 localhost run-parts(/etc/cron.hourly)[18679]: finished 0anacron
Sep 12 11:01:01 localhost run-parts(/etc/cron.hourly)[18670]: starting 0yum-hourly.cron
Sep 12 11:11:56 localhost run-parts(/etc/cron.hourly)[18952]: finished 0yum-hourly.cron
Categories: CentOSLinux

Leave a Reply

Your email address will not be published. Required fields are marked *

Related Posts

Application Containers

Docker container management using Rancher

What is container management and why to use it?A container management platform is a solution used to o create cloud-native, distributed applications and package legacy applications that were not originally designed for virtual environments. Container Read more…

CentOS

Install MySQL Galera Cluster on Centos 7

What is MySQL cluster and how to use it?MySQL Galera Cluster is a synchronous multi-master cluster, available on Linux only, and only supports the XtraDB/InnoDB storage engines . It is designed to provide high availability Read more…

Application Containers

Installing Docker on Centos 7

What are Docker containers and how to use them?Docker is a software technology providing containers. Docker provides an additional layer of abstraction and automation of operating-system-level virtualization on Windows and Linux. Docker uses the resource Read more…