Sunday, August 17, 2008

Virtualization, RHEL 5.1

RHEL 5.1 will bring hardware virtualization feature improvements, paravirtualized drivers, the Xen 3.0.5 hypervisor and features like non-uniform memory access (NUMA) topology and loopback removal. Also, 5.1 will support live moves of virtual machines in clusters, along the lines of the functionality of VMware's VMotion.

Users of older versions of Red Hat are not being left out of the virtualization loop. Red Hat added some Xen support features to Red Hat Enterprise Linux 4.5.

The 4.5 option will have limitations. RHEL 4.5 includes virtualization support, so you have the choice of full virt or paravirt. Anything prior to RHEL 4.5 will run out of the box but will need full virtualization. You'll need a new chip. You don't have to touch the code, but you won't get the performance you get with RHEL 5.

VMware is way ahead of all the others in features and robustness, but VMware doesn't have a product that scales well. There are definitely limitations in high-availability, so most people are just virtualizing file servers at this point and not databases and performance-intensive apps.

To get the most out of RHEL 5's virtualization support options, these recommendations:

* Secure RHEL 5 platform layer before installing any virtual machines or applications.
* Run SELinux to run in enforcing mode.
* Remove or disable any unwanted services, like AutoFS, NFS, FTP, WWW, NIS, telnetd, sendmail and so on.
* Only add the minimum number of user accounts needed for platform management.
* Avoid running applications on dom0/Hypervisor, because running apps in dom0 may impact virtual machine performance.
* Use a central location for a virtual machine installation, which will make it easier to move to shared storage later on.

Tuesday, August 12, 2008

Postfix(MTA) appln corrupt ( OS: RHEL4)

If your postfix (MTA) stopped working or corrupt and not sure how to upgrade or downgrade it for better performance???

Here follows the solution for that :

step 1 : Query installed appln to know version details ( use following command )

command # rpm -qi postfix

step 2: Search for updated RPM of Postix ( if have subscription use and download to local machine

step 3: Query to list postfix related files using following command as a root

command# rpm -ql postfix

step 4: better backup files ( output of above command ) which are essential like, Configuration files /etc/postfix and mail queue /var/spool/postfix using command {cp -a source destination}

step 5: simulate RPM package installation before installing to machine. This will help to identify dependances error and file conflicts error.

command # rpm -Uvh --test postfix-2.2.x-RHEL.rpm

step 6: If found no error on above command , Now you can go for installing RPM using following command

command # rpm -Uvh postfix-2.2.x-RHEL.rpm

step 7 : To release mail queue built on the system when MTA was corrput. we need to requeue mails to flow again by following command

command # postsuper -r ALL

step 8 : Give a look on maillog to check for mail delivery to domain.

command #tail -f /var/log/maillog

Note : if you want to downgrade MTA, use this command instead of step 5 and rest of steps are same.

command # rpm -Uvh --test --oldpackage postfix-2.2.x-RHEL.rpm

command # rpm -Uvh --oldpackage postfix-2.2.x-RHEL.rpm

Thursday, August 7, 2008

Troubleshooting Tools: Diagnosis DNS

In this Troubleshooting Tools for DNS, Given a record name, and a record type, you will receive a report detailing all possible answers. This is accomplished by traversing the DNS tree from the root examining all possible routes that a client could travel, calculating percentage probabilities on the way.

Visit DNS checker... :

Red Hat Linux Tips and Tricks

We know that top is a very powerful tool for monitoring running processes. Now we investigate the power of mutliple sections during an active session of top.

1. At the command-line, type top.
2. Activate multiple sections by using "shift+a"
3. The interface will now display four sections. Use the lower-case "a" to toggle between sections. Notice in the top left hand corner you will see the active section identifier: 1:Def, 2:Job, 3:Mem, 4:Usr
4. To add color to section 1:Def.
1. Press "a" to toggle to section 1:Def.
2. Press "z" to toggle color on and off. Notice that you can toggle from one section to the other to add a different color scheme to each section.
5. Highlight the sort fields in section 1:Def.
1. Press "a" to toggle to section 1:Def.
2. Make sure color is activated by pressing "z".
3. Press ""x" to toggle the highlight feature of the sort fields. You may not recognize the highlighting right away, but by holding down the left Shift key and using the < and > keys, you can move the sort field left and right respectively.

Red Hat Linux Tips and Tricks

We know that the out-of-the-box resources should be a primary tool of any system administrator. We also know that navigating from one node to the other using "info" in search of information can be frustrating.

For example, you want information on configuring grub.conf. You find that running the command "info grub" displays a long menu of options, including one that applies to configuration. You get there by using the hypertext navigation method, placing the cursor on the line that reads "* Configuration" and then hitting the ENTER key.

How would you slice out or print just the "Configuration" node to file?

Answer: If you would like to print the Configuration node to a text file, run the following command:

# info grub Configuration -o mynewfilename.txt

You now have a single text file named "mynewfilename.txt" with the information from the Configuration node of info. This can be done with any node you would like to slice out of info pages into a more manageable and specific text file.

Monday, August 4, 2008

All you have to know about RPM

The RPM Package Manager ( is a powerful command line driven package management system capable of installing, uninstalling, verifying, querying, and updating computer software packages.
RPM is free software, released under the GNU GPL.RPM is a core component of many Linux distributions, such as Red Hat Enterprise Linux, the Fedora Project, SUSE Linux Enterprise, openSUSE, CentOS, Mandriva Linux, and many others. It is also used on many other operating systems as well, and the RPM format is part of the Linux Standard Base.

For simply install a package do:

rpm -i package.rpm

Where "-i" is the Install parameter and "package.rpm" is the RPM you're installing. You can add more parameters to the above command,try this:

rpm -ivh package.rpm

The "-v" is for verbose and "-h" for the hashing marks. It'll print some "#" when unpacking and then installs the package. You can use "--percent" instead of "-h" if you want.

The above command is maybe the first RPM command you've learned. Upgrading to a New package can be done in 2 ways, the Freshen way and by executing:

rpm -Uvh new-package.rpm

Note that the "-U" Upgrading option simple removes the old and installed package, then install the new one. The "-Uvh" can be used to install a package too, if the package does not exist on your system the new-package.rpm will be installed.

Now imagine the situation where the new version of Samba you've just installed is not compatible with your applications, what to do? Answer: Upgrade to the old version. You can call this a "Downgrade" if you want. The command for install the Old package will be:

rpm -Uvh --oldpackage Samba-old-version.rpm

Where "--oldpackage" option says that Samba package version is older than the one installed. The command will remove the installed version and then install the Samba-old-ver.rpm.

For More hands on Refer To :