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Performance Monitoring

Here are some handy commands that I used recently to debug a server performance issue:

Also “sar -A” give more useful info.

For sar to work, you need a cronjob like this:

The cronjob can go in a file at /etc/cron.d/sysstat on Redhat and similar systems.

Another useful command is “vmstat”:


Preferences vs. Command Line Options

Here’s my question answered by the author of DSpam – Jonathan Zdziarski:


Relay Control

In qmail, relaying is usually controlled by the tcpserver wrapper which uses a config file at either /etc/tcp.smtp or /home/vpopmail/etc/tcp.smtp.

The config file must be compiled into a binary format – “tcp.smtp.cdb” for actual use. Here’s the command line:

You don’t need to restart qmail after rebuilding the database.


Squid Guard

We’ll start by installing Squid:

Squid is now installed at /usr/local/squid.

Notice that we use the “wget” command to download the software. Then we unpack and build the software. The build sequence is very typical for Linux packages – configure, make, make install.

We finish up by saving the distribution to /root/archive and removing the build
directory that is no longer needed.

Configuration for squid is pretty simple in the basic case. All configuration is
stored in a single file located at /usr/local/squid/etc/squid.conf.

The squid.conf file can be edited with your favoriate text editor. All though there
are hundreds of configuration options only a few are needed in a basic install. We made the following changes:

a. Find the line that looks like this (approx line 684):

Remove the “#” comment from the begining of the line and set the desired cache size and location:

This defines a cache of not more then 768MB of disk storage.