How to clear cache on Linux

In this article, we will guide you how to clear the memory cache on Linux system by clearing PageCache, dentries, and inodes from the command line.

In linux system basically we have a three different type of caches that need to be clear from linux system.

PageCache is cached files. Files that were recently accessed are stored here so they will not need to be queried from the hard disk again, unless that file changes or the cache is cleared to make room for other data

Dentry, inode cache is directory and file attributes. This information goes hand in hand with PageCache, although it doesn't contain the actual contents of any files.

Please find the below commands to clear the cache from linux device

To clear PageCache only, use this command:-

[root@localhost:~]#sysctl vm.drop_caches=1

To clear dentries and inodes, use this command:-

[root@localhost:~]#sysctl vm.drop_caches=2

To clear PageCache, plus dentries and inodes, use this command:-

[root@localhost:~]#sysctl vm.drop_caches=3

Please use free command or top to check your system's RAM usage and verify that the cache has been cleared.

Also you can use the following commands to accomplish the same thing as the respective systemctl commands:

Clear PageCache:-

[root@localhost:~]# echo 1 > /proc/sys/vm/drop_caches 

Clear dentries and inodes:-

[root@localhost:~]# echo 2 > /proc/sys/vm/drop_caches 

Clear PageCache, dentries and inodes:-

[root@localhost:~]# echo 3 > /proc/sys/vm/drop_caches

Using above commands you can clear the cache from linux system. In case you have any query please comment on this post. Thanks!!

Puppet agent: Exiting; no certificate found and waitforcert is disabled

Puppet agent: Exiting; no certificate found and waitforcert is disabled - 

Such type of error coming when puppet agent connecting to a Puppet master server for a first time will generate a certificate and give it to a Puppet master server to sign.

Basically its depend upon your puppet configuration, a default behavior is that the certificate must by signed manually and thus puppet agent exits with an error.

[root@puppet-client:~]#puppet agent -t

Exiting; no certificate found and waitforcert is disabled

To resolve this issue login to the Puppet master server and run the below command to list all certificates awaiting a signature.

[root@puppet-master ~]# puppet cert list

"puppet-client"      (SHA256)

B3:67:17:66:8E:78:1F:69:4E:11:8E:34:BA:86:A0:E7:07:84:BF:E9:8A:94:A9:41:DD:6C:9D:1B:07:D2:72:6A

From the above output we can see that certificate from a single host puppet-client is waiting for its certificate to be signed. 

Note: Your output may be different and contain multiple certificates awaiting for a signature.

Now we have two options on how to sign the above certificate. 

Option 1: We can sign each certificate individually.

Option 2: We can sign all awaiting certificates at once.

For option 1 , please run the below command 

[root@puppet-master ~]# puppet cert sign puppet-client

For Option 2, please run the below command

[root@puppet-master ~]# puppet cert sign --all

Using above option you can remove such errors. Now login on the puppet-client machine and run the puppet agent again.

[root@puppet-client:~]#puppet agent -t

Now you will not receive certificate error. In case you have any query on above article, please comment on this post. Thanks!!