Urdu CBT Linux System Administration qmail 1/7

It explains how you can configure qmail SMTP server (written by Dan Bernstein), with all the bells and whistles, using steps outlined by the creator of qmailrocks.com website (now de-functional). The qmailrocks guide was somewhat in-sufficient in explaining how qmail actually works. It just spoon-feeds you the steps to do (copy/paste). I was learning qmail myself when I created these CBTs, so there are areas in this CBT which are weak. I don’t recommend this CBT to be used to setup a production qmail server. It has only been uploaded for archiving reason. If you really want to learn qmail, the best sources are “Life with Qmail” and John Simpson’s “http://qmail.jms1.net/” .

Author: Muhammad Kamran Azeem
Courtesy: http://wbitt.com

Installing Nagios core on RHEL / CENTOS 5.x – RHEL / CentOS 6.x Fedora 15/16/17/18/19/20

What is Nagios

An enterprise-class monitoring and alerting solution that provides organizations with extended insight of their IT infrastructure before problems affect critical business processes.

Requirements

We require following things for Installing Nagios:
These are Just Pre-requisites. We need them to other things work …

1. Apache and PhP (php is optional)
2. gcc, glib, glibc-common, gd and gd-devel

Continue reading “Installing Nagios core on RHEL / CENTOS 5.x – RHEL / CentOS 6.x Fedora 15/16/17/18/19/20”

Postfix Mail Delivery SMTP Troubleshooting

To avoid delay in emails, specially for gmail. Just find which MX is working by issuing below commands:

# dig mx gmail.com

# telnet mx-IP/name 25

upon success, just see the name of first mx tried from /var/log/maillog

and add an entry in /etc/hosts file.

In my case, the entry is given below:
# vim /etc/hosts

74.125.25.26 aspmx.l.google.com
74.125.25.26 alt1.aspmx.l.google.com
74.125.25.26 alt2.aspmx.l.google.com

:save and exit

now open postfix main.cf and add smtp_host_lookup directive under inet_protocols = all

# vim /etc/postfix/main.cf

inet_protocols = all
smtp_host_lookup=native
save and exit

now restart postfix

# service postfix restart

by default postfix host lookup is done via DNS, native mode uses nsswitch.conf settings and will check /etc/hosts first and then DNS if entry not found in /etc/hosts