When dealing with SMTP for the RHCE or LFCE exams, there are some tips that can be very useful to know about Postfix.

First, you’ve got a very interesting website at http://www.postfix.org/postfix-manuals.html.

Then, during the exam, you can get some configuration examples in the /usr/share/doc/postfix-2.10.1/README_FILES directory for RHEL 7 (-/postfix-2.6.6/README_FILES for RHEL 6) in the BASIC_CONFIGURATION_README and STANDARD_CONFIGURATION_README files. This documentation comes with the postfix package.

In addition, the /etc/postfix/main.cf file, the main configuration file, is fully documented. This will help you decide what parameter to change.

But there are more to know!
You’ve got the choice to edit the /etc/postfix/main.cf file or to use the very powerful postconf command. Instead of wasting time, searching for the Postfix parameter in the main.cf file, if you know its name, you can directly assign a value to it or get its value:

# postconf -e 'relayhost=[192.168.1.1]'
# postconf relayhost
relayhost = [192.168.1.1]

This is not only very efficient, but the configuration is also definitively written in the main.cf file!
You can restart the Postfix processes or even reboot the server, it’s still there.

Also, by using the relayhost = [192.168.1.1] syntax during your test, you can avoid the use of a master DNS server and its associated MX record (MaileXchange), which can be very handy.

Finally, at any time, you can check the syntax of the main.cf file with the postfix check command.
You can also get the list of the parameters with non-default assigned values with the postconf -n command.

In conclusion, Postfix is really a powerful and well designed tool.

One week after the CentOS 7 rolling builds announcement, one day after the Fedora 21 release, it’s now the RHEL 7.1 Beta that is unveiled!

This minor release brings many new improvements.
Lots of them are summed up in the article about the RHEL 7.1 changes.

Happy reading!

Yesterday, Red Hat published a post concerning RHCSA & RHCE 6 exams availability.

According to this post, candidates have one year to take RHCSA 6 or RHCE 6 exams as Individual Exam Sessions under the condition that they purchase the vouncher before February 28, 2015.

If you plan to take the RHCSA 6 or RHCE 6 exams, you’ve got to hurry because these exams will be withdrawn in two to three weeks.

As RHCSA 7 is not too different from RHCSA 6, it will not be too painful if you miss the date.

It’s going to be an other song if you wanted to take the RHCE 6 exam, because the v7 is an other world: you will have to start almost from scratch! Firstly, it’s now 3.5 hours instead of 2. Secondly, topics are different: network (teaming, bonding, ipv6, etc), Kerberos (NFS+Samba), security (firewalld), storage (iSCSI), and database (MariaDB).

If you thought about taking the RHCE 6 exam, book it now and work hard to pass it at the first attempt!

Since RHEL 6, a transaction history has been added to the yum command.
This feature allows you to precisely know which packages have been installed on a server and in which order.
In addition, you can undo or redo any of the previous package installations.
Finally, by comparing the rpmdb version of two servers, you can verify if the exact same packages have been installed on both of them, which can be useful when moving from development to production environments.
To get into the details, check the tutorial about using the yum transaction history.

If you need to configure a server for a specific task (for SAP, with reduced network latency, for maximum throughput, as a desktop, as a virtual host, etc), a dedicated tool already existed in RHEL 6: tuned-adm.

This tool still exists in RHEL 7 and in an enhanced version. If you want to know more, a dedicated tutorial on tuned-adm is now available.

In one of his latest videos Sander van Vugt shows us that some SELinux information is not available without some tricky operations.

Actually, after a standard RHEL 7 / CentOS 7 installation, only basic SELinux man pages are installed. All the SELinux man pages dealing with applications (httpd, vsftpd, etc) need an additional work to be accessible.

Now, you’ve got two options: watch Sander van Vugt’s video or access my dedicated tutorial about deploying additional SELinux man pages. It’s up to you!

Yesterday, Red Hat announced the official release of RHEL 6.6.

This minor version brings several improvements:

• The scap-security-guide package has been added providing a convenient and reliable way to verify system compliance on a regular basis,
• The KeepAlived and HAProxy packages are now fully supported,
• The System Security Services Daemon (SSSD) package has been updated to make Linux-Windows integration easier: you can now enable a cross-realm Kerberos trust through a RHEL 7 server,
• The Performance Co-Pilot (PCP) framework for performance monitoring and management has been added: you can now monitor performance across a set of RHEL 6 and 7 servers in a single, consistent approach,
• The OpenJDK 8 is now available as a technology preview,
• Various performance improvements coming from RHEL 7 have been also backported.

Sources: Red Hat 6.6 Release Notes and Red Hat 6.6 Technical Notes.