How to Clear RAM Memory Cache, Buffer, and Swap Space on a Check Point Firewall

September 21, 2020 David Barker David Barker

4 Min Read

Does your firewall seem like it is always low on memory?  Does it get sluggish at times and seem unresponsive or less responsive?  It might be because your firewall is swapping memory to disk.  Since read and write operations to disk are much slower than to memory, performance suffers greatly.  If rebooting the firewall seems like the only fix, you might benefit from the information below.

Like other operating systems, a Check Point Firewall has an excellent memory management system implemented. However, occasionally processes eat away at the memory, and thankfully there is a relatively straightforward process to clear it in the underlying Gaia operating system.

First, determine if there is a problem with the cache or swap space on your Check Point Firewall.

From the expert-prompt, or bash-prompt, type the command. 

free -m” 

If your firewall could benefit from clearing the caches, it should return something like this. 

[Expert@horrafw01:0]# free -m

             total       used       free     shared    buffers     cached

Mem:          7731       7291        440          0        231       1063

-/+ buffers/cache:       5997       1734

Swap:        20512       1495      19017

From this listing, you can see that the memory is pretty full, with only 440M free, and the firewall has started to consume Swap.   But there are 1063M in Cache, and this is our target to free memory.

A brief explanation of the cache is as follows.  This number represents three caches, page, inode, and dentry caches.  Gaia keeps a page cache in otherwise unused portions of the main memory (RAM), resulting in quicker access to cached pages and overall performance improvements.  Similarly, the inode cache and dentry cache hold recently accessed files and directories on the server.  As time goes on, these caches can grow quite large, especially on a busy firewall.  The cache is more than one gig of the eight gigs of memory the firewall has in the example above.  The lack of available memory has caused this firewall to swap to disk.  

Let’s run the following command and see if we can reclaim some memory.  The “3” in the following command clears the page cache, dentry cache, and inode caches.  

“echo 3 > /proc/sys/vm/drop_caches”

“free -m”

[Expert@horrafw01:0]# echo 3 > /proc/sys/vm/drop_caches

[Expert@horrafw01:0]# free -m

             total       used       free     shared    buffers     cached

Mem:          7731       6049       1682          0          0         89

-/+ buffers/cache:       5959       1772

Swap:        20512       1495      19017

We’ve now freed memory from the cache and have 1682M free up from 440M free.  Since this amount is greater than the amount swapped to disk, we should be able to free the swap space.

Let’s try freeing the swap memory now.  

The following command will just turn off the swap and turn it back on.

“swapoff -a && swapon -a”

[Expert@horrafw01:0]# swapoff -a && swapon -a

Rerunning the command “free -m” will confirm that we’re using 0 swap now. 

[Expert@horrafw01:0]# free -m

             total       used       free     shared    buffers     cached

Mem:          7731       6849        881          0          2         98

-/+ buffers/cache:       6748        982

Swap:        20512          0      20512

To summarize, on this firewall, we could clear swap space and free memory from caches using a series of commands, but these could be combined into one command. 

“echo 3 > /proc/sys/vm/drop_caches && swapoff -a && swapon -a”

This simple one-line command could quickly be scheduled to run every night to keep your firewall memory clear.

First, create a shell script clearcache.sh in /home/admin (or another directory) and add the following lines.

#!/bin/bash

echo 3 > /proc/sys/vm/drop_caches 

swapoff -a 

swapon -a

Next, set execute permissions on the file with “chmod 755 /home/admin/clearcache.sh”

Now from the clish prompt, schedule this to run nightly at 2 am. (or whatever your least busy time is)

> add cron job clearcache command /home/admin/clearcache.sh recurrence daily time 2:00

This should add a cron job called clearcache that runs every night at 2:00 am. 

Verify that it has been scheduled with the following commands

> show cron job clearcache command

/home/admin/clearcache.sh

> show cron job clearcache recurrence

Every day at 2:00

Obviously, this isn’t going to fix a firewall that has too little memory to be functional. However, if you noticed that your firewall’s memory increases over weeks and months without rebooting, this might just be the fix that you’ve been looking for. 

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