How to Clear the Linux Memory Cache
Clearning the Linux Memory cache can be a quick way to regain system resources. Writing to the drop_cache process will cause the kernel to drop clean caches, dentries and inodes from memory, causing that memory to become free.
- To free pagecache:# echo 1 > /proc/sys/vm/drop_caches
- To free dentries and inodes:# echo 2 > /proc/sys/vm/drop_caches
- To free pagecache, dentries and inodes:# echo 3 > /proc/sys/vm/drop_caches
As this is a non-destructive operation, and dirty objects are not freeable, the user should run "sync" first in order to make sure all cached objects are freed.
Example - Memory before:
[root@server ~]# free -m
total used free shared buffers cached
Mem: 7860 7040 820 0 343 5076
-/+ buffers/cache: 1620 6240
Swap: 3999 0 3999
[root@server ~]# sync
[root@server ~]# echo 3 > /proc/sys/vm/drop_caches
Memory after:
[root@server ~]# free -m
total used free shared buffers cached
Mem: 7860 1279 6581 0 0 33
-/+ buffers/cache: 1245 6615
Swap: 3999 0 3999
Import an OpenSSL CSR into Windows CA server
To import a Certificate Signing Request (CSR) into a Windows Certificate Authority Server, you must define a certificate template. OpenSSL does not do this because this is a Microsoft only concept. With the use of the Windows 'certreq' command, you can apply a template type during the request import process. This command should be available on your Microsoft CA server.
C:\>certreq -submit -attrib "CertificateTemplate:WebServer" request.csr
An alternative method for importing CSR's to Microsoft CA can be found here.
Plesk Qmail Error 5.4.6
I recently ran into a strange problem with Plesk 9.3 and Qmail. After completing the install of a new Plesk server I initiated migrations of production sites to it. Post migration the sites and email functioned normally for around 22 hours until suddenly all inbound email to the server bounced with the following error:
Nov 6 05:50:29 vh1 qmail-[27612]: Handlers Filter before-remote for qmail started ...
Nov 6 05:50:29 vh1 qmail-[27612]: from=m@me.com
Nov 6 05:50:29 vh1 qmail-[27612]: to=add2@domain.com
Nov 6 05:50:29 vh1 qmail-[27612]: hook_dir = '/usr/local/psa/handlers/before-remote'
Nov 6 05:50:29 vh1 qmail-[27612]: recipient[3] = 'add2@domain.com'
Nov 6 05:50:29 vh1 qmail-[27612]: handlers dir = '/usr/local/psa/handlers/before-remote/recipient/paul@tap10.com'
Nov 6 05:50:29 vh1 qmail: 1320533429.707838 delivery 233: failure: Sorry._Although_I'm_listed_as_a_best preference_MX_or_A_for_that_host,/it_isn't_in_my_control/locals_file,_so_I_don't_treat_it_as_local._(#5.4.6)/
The problem could be resolved by simply restarting Qmail but then the issue re-occured 22 hours later, immediately after nightly backups.
Parallels notes a fix for the problem at: http://kb.parallels.com/en/1380 but after running /usr/local/psa/admin/sbin/mchk then waiting 22 hours, the problem re-occurred.
Cisco IOS Diagnostic Tools
There are certain a number of diagnostic tools that can be used to troubleshoot and monitor the different elements of a network. This article takes a look at a number of the built-in tools/command that exists within Cisco IOS. Any experienced IOS engineer knows that many issues can be diagnosed using only the tools that exist within the IOS itself; the target audience of this article includes engineers with less experience looking to become more familiar with the available tools and those preparing for the CCNP TSHOOT exam.
Show Processes CPU
One of the most basic commands to run on a Cisco device is show processes cpu. In its full view the command will show all of the active processes on a device and how much of the processor time the process is taking both currently and historically. Figure 1 below shows a shortened version of the command:
This command would typically be used when troubleshooting a problem with a device that is having trouble performing basic functions; for example if a router is having trouble forwarding and routing pa