Tag Archives: linux

MySQL: Migrating Slave to New Master

Consider the following scenario:
Master’s IP address has been changed and the slave needs to be reconfigured for the New IP address.

How do we go about doing it ? Two ways.
One of them a bit hackish but the most

– Shut down slave MySQL server.
– Find master.info file, store current one in the backup and edit it
replacing the host name with new host name.
– Start slave MySQL server.

Second one is more complex but using only SQL commands:

– Run SLAVE STOP to stop slave thread;
– Run SHOW SLAVE STATUS and record the position in the master binary log
slave is currently located
– use CHANGE MASTER TO to point slave to the same position on the
different hostname
– Use SLAVE START to start slave back again.

We cannot change the IP that easily. We need to do things so complex since MySQL assumes we are
replicating from new slave if you’re changing host name and resets all
other parameters.

Configuring MRTG and NET-SNMP for monitoring Linux System Parameters

MRTG ver. 2.97
Net-SNMP ver. 4.2.6
OS : RedHat Linux 7.3

This doc should help you with configuring a RedHat Linux box for monitoring system parameters (local/remote), using Net-SNMP and MRTG.

About MRTG and Net-SNMP

MRTG (Multi-Router Traffic Grapher)
The Multi Router Traffic Grapher (MRTG) is a tool to monitor the traffic load on network-links. MRTG generates HTML pages containing graphical images which provide a LIVE visual representation of this traffic.
Check http://www.ee.ethz.ch/stats/mrtg/ for an example.
MRTG is based on Perl and C and works under UNIX and Windows NT.
MRTG is being successfully used on many sites around the net


Net-SNMP is a collection of various tools relating to the Simple Network Management Protocol including:

* An extensible agent
* An SNMP library
* tools to request or set information from SNMP agents
* tools to generate and handle SNMP traps
* a version of the unix ‘netstat’ command using SNMP
* a graphical Perl/Tk/SNMP based mib browser

Continue reading Configuring MRTG and NET-SNMP for monitoring Linux System Parameters

Installing Spamassassin for filtering Spam

Note: This document is only for per-user configuration of spamassassin

Configuration: RedHat Linux 7.2, Sendmail 8.12.6, procmail 3.21, SpamAssassin 2.43 ( and you will have to be connected to the internet)

Installing the prerequisites:
Spam assassin depends on other perl modules. The complete SpamAssassin package along with its dependent modules can be installed using CPAN:
as root:
# perl -MCPAN -e shell
install Mail::SpamAssassin

If CPAN has been configured properly, this should be a successfull install. SpamAssassin is now installed in /usr/bin/SpamAssassin.

We would be using procmail to filter messages. Due to sendmail’s security feature, we would have to create a symlink to procmail in the director /usr/adm/sm.bin
# cd /usr/adm/sm.bin
# ln -s /usr/bin/procmail ./procmail
( sendmail executes the programs, only when they are symlinked to, in /usr/admin/sm.bin)

Configuring SpamAssassin ( for user, say, ram)
1) Make sure that your home root directory ( /home) and your home directory ( /home/ram) is not group writable.
2) create a file in your home directory, ~ram/.forward, and add the follwing to it:
“|/usr/bin/procmail -f- #ram”

3) now, this ~ram/.forward file should have permission of 700
4) create a file called spams in your home directory
5) create file, ~ram/.procmailrc with the following content:
| /usr/bin/spamassassin
* ^^rom[ ]
LOG=”*** Dropped F off From_ header! Fixing up. ”

:0 fhw
| sed -e ‘1s/^/F/’

( Here, we are processing the incoming mail using SpamAssassin, and if the mail is marked by SpamAssassin as a spam, we move it to a file called spams. The third rule is a workaround for a bug in procmail 3.21)

6) Send a test mail to yourself. you should now see the following in your mail header:
X-Spam-Status: No, hits=2.6 required=5.0
X-Spam-Level: **
X-UIDL: 5,@!!fXk!!`Cm”!6?l”!M

7) You can now configure your mail client to parse the headers and check for X-spam-Status = Yes, throw into a seperate folder , or use procmail to do it, by adding:
* ^X-Spam-Status: Yes
as your second rule.