Archive for the 'tips and tricks' category

Building software in most languages is a pain. Remember ant build.xml, maven2 pom files, and multi-level makefiles?

Python has a simple solution for building modules, applications, and extensions called distutils. Disutils comes as part of the Python distribution so there are no other packages required.

Pull down just about any python source code and you’re more than likely going to find a setup.py script that helps make building and installing a snap. Most engineers don’t add functionality when using distutils, instead opting to use the default commands.

In some cases, developers might provide secondary scripts to do other tasks for building and testing outside of the setup script, but I believe that can lead to unnecessary complication of common tasks. » Read more

1.) Firstly, lock the account to prevent the user from using the login until the change has been made:

# usermod -L

2.) Change the password expiration date to 0 to ensure the user changes the password during the next login:

# chage -d 0

3.) To unlock the account after the change do the following:

# usermod -U

» Read more

Answer:

The raw devices interface has been deprecated in Red Hat® Enterprise Linux® 5. The rawdevices service and /etc/sysconfig/rawdevices file no longer exist and raw devices are now configured via udev rules. However the preferred method for performing raw I/O (ie. bypassing filesystem caching) is to open EXT3/EXT2 files with the O_DIRECT flag.

This is an excerpt from the raw command’s man page:

Although  Linux  includes  support  for rawio, it is now a deprecated interface. If your application performs device access using this
interface, Red Hat encourages you to modify your application to open the block device with the O_DIRECT flag. The rawio interface will
exist for the life of Red Hat Enterprise Linux 5, but is a candidate for removal from future releases.

» Read more

Devlabel is a script which manages symbolic links to storage devices on your system. This is accomplished by utilizing the inherent unique identifiers (UUID) that each device should have in order to maintain a correctly pointing symlink in the event that the device name changes (eg. /dev/sdc1 becomes /dev/sdd1).
» Read more

Question: How do I register my Red Hat Enterprise Linux Xen Guest system with the Red Hat Network?

Answer:

Important: For Red Hat Enterprise Linux 4 fully-virtualized guests install the latest version of up2date.

This procedure will work for both fully-virtualized and para-virtualized guests.

1. The host system (dom0) must be registered with Red Hat Network. Follow standard procedures to register this system with Red Hat Network (RHN).
2. Under the System Properties page, subscribe the base system to the appropriate Virtualization Channel. Virtualization allows for up to 4 Xen guest registrations, while Virtualization Platform allows for an unlimited number of Xen guest registrations.
3. Make sure that the virtualization add on entitlement is checked “Add-On Entitlements: Virtualization *(0 open entitlements)*”. This is available via rhn.redhat.com –> Systems (Top Red Bar) –> Click on the host
   system –> Click Edit These Properties –> Check the add on entitlements
   box (Virtualization) –> Click update properties. If you have Advanced
   Platform entitlement you can check the “Virtualization Platform” box
   instead to be able to register an unlimited number of guests for this host.

4. Make sure that rhn-virtualization-common and rhn-virtualization-host are installed on the host system. If they are not installed, run:

   yum install rhn-virtualization-common rhn-virtualization-host
   

5. Install the Xen guest.
6. Make sure that the Xen guest is running. Please note that xenguest is the name of the Xen guest.

   xm create xenguest
   

7. From the command line on the host system, run:

   rhn_check
   

8. From the command line on the host system, run:

   rhn-profile-sync
   

9. From the Xen guest, run:

   rhn_register
   

Now the Xen guest will show up as a registered, virtualized system. » Read more

Question: I recently used up2date to get the latest kernel for my Red Hat Enterprise Linux 3 system and now I have found out that I need an older version for my application that needs kernel 2.4.21-x. How do I download and install a different or an older kernel version then the one I got from Red Hat Network (RHN)? » Read more

With many Red Hat Enterprise Linux 4 to Red Hat Enterprise Linux 5 upgrades, the rhnsd service was disabled. To re-enable this service, perform the following steps:

# chkconfig --add rhnsd
# chkconfig rhnsd on
# service rhnsd start

Question: After downloading and burning ISO files from Red Hat Network (RHN) why will the system not boot from the first burned CD?

Answer:

First, make sure that you have downloaded the correct files. For each distribution there are binary files and source files. To complete an installation the four binary files for a particular distribution are required.

Simply burning these files to CD as files will result in a single file being burnt to CD with a .iso extension. If this occurs your disks will not be bootable. The files available from Red Hat Network (RHN) are disk images and need to be burned to CD as an image.

Your burning software will extract the files from the .iso and burn them to CD. See your specific burning software documentation for more information on how to burn images to CD.

To check if you have burned each image correctly, simply examine the contents of the CD. Instead of a single .iso file the disk should contain multiple files and directories. » Read more

Question: Is there an alternative module to the mod_jk module that is provided in the standard channel for Red Hat® Enterprise Linux® 5?

Answer: The module mod_jk is currently included as part of the Application Stack channel and is not available in the base channel. However in Red Hat Enterprise Linux 5, the package httpd does provide a module by the name mod_proxy_ajp which helps connect between the two. The configuration file is located at /etc/httpd/conf.d/proxy_ajp.conf. Edit this configuration file according to the needs of the enviroment. At the very least, add i the webapps directory used by tomcat:

<pre class = “screen”
     ProxyPass /tomcat/ ajp://localhost:8009/
     ProxyPass /examples/ ajp://localhost:8009/jsp-examples/
» Read more

Unlike Red Hat Enterprise Linux versions 2.1 and 3, there is no kernel-source package in the Red Hat Enterprise Linux 4 distribution. It was deemed redundant to provide a kernel-source package and a kernel .src.rpm package at the same time. Users that require access to the kernel sources can find them in the kernel.src.rpm file.

In Red Hat Enterprise Linux 4, The kernel-devel package includes the kernel headers files and you no longer require the kernel source package to build a third party kernel module. To install the kernel-devel package run the following command as root user in a terminal:

#up2date kernel-devel

A full source tree is not required in order to build modules against the current kernel you are using. You can simply point your Makefile to /lib/modules/`uname -r`/build. A more detailed explanation can also be found in the Release Notes. » Read more