The Panic Room

Compiling OpenLDAP on Debian Lenny

Chamila | පිටස්තරයා — Mon, 16 Aug 2010 19:07:40 +0000

Download the latest OpenLDAP source from the site (http://openldap.org).

Go to /usr/src/ and untar the source package.

tar xzvf openldap-stable-20100719.tgz cd openldap-2.4.23

Then install the following prerequisites that are needed to compile OpenLDAP.

apt-get install build-essential cyrus-sasl2-dbg openssl libtool libdb-dev gnutls-dev libsasl2-dev

Then start compiling OpenLDAP.

./configure make depend make make test make install

OpenLDAP Should be working now.

For configuration files, look in /usr/local/etc/openldap/.

Uninstalling such an installation is a bit of pain in the ass. OpenLDAP does not have a make uninstall defined. So, the files have to be manually deleted.

To identify which files are to be deleted, do an install to a temporary directory and note down the files.

make install DESTDIR=/tmp/ldap/

Enabling mod_rewrite in Apache2 (LAMP)

Chamila | පිටස්තරයා — Thu, 12 Aug 2010 04:24:18 +0000

mod_rewrite is a module in Apache which is used to simply rewrite a URL into a different URL. This module comes by default with Apache2. If you are using Apache in a Windows environment, simply right clicking on the Wamp server icon and enabling mod_rewrite from there would do. But in a Linux environment, these are the simple steps to follow.

Issue the following command to enable the module.

a2enmod rewrite

The command a2enmod can be used to load this kind of modules to Apache.

Chances are that you would still not be able to have URL rewrites. For this you must change some settings in another conf file.

Go to /etc/apache2/sites-available/ and open the file default. Replace every “AllowOverride None” with “AllowOverride All“. This enables Apache2 to override rewrites by the use of .htaccess files.

Restart the server and rewrites should be working fine for you.

/etc/init.d/apache2 restart

Installing Xen on Debian Lenny – Binaries

Chamila | පිටස්තරයා — Tue, 10 Aug 2010 08:49:14 +0000

Update and upgrade the system.

apt-get update && apt-get upgrade -y

Then install the following packages.

apt-get install xen-linux-system-2.6.26-2-xen-amd64 linux-modules-2.6-xen-amd64

xen-linux-system-2.6.26-2-xen-amd64 installs the following packages.

linux-image-2.6.26-2-xen-amd64
xen-hypervisor-3.2-1-amd64

This installation will create the Xen kernel at /boot and add the proper entries to the /boot/grub/menu.lst. Check your menu.lst and set the Xen kernel as the booting kernel.

vi /boot/grub/menu.lst

Check whether your Xen kernel entry is something similar to the following.

title Xen 3.2-1-amd64 / Debian GNU/Linux, kernel 2.6.26-2-xen-amd64 root (hd0,2) kernel /xen-3.2-1-amd64.gz module /vmlinuz-2.6.26-2-xen-amd64 root=/dev/sda1 ro console=tty0 module /initrd.img-2.6.26-2-xen-amd64

Set the booting kernel number by changing the default line. And reboot.

After logging in check whether the Xen daemon (xend) is running. Then issue the following command to make sure Xen is running properly.

xm list

It should output something like this.

Name ID Mem VCPUs State Time(s) Domain-0 0 14711 8 r----- 5205.1

Xen Dom0 Fails to boot. Error “elf_init: not an ELF binary”

Chamila | පිටස්තරයා — Sun, 08 Aug 2010 09:59:15 +0000

Recently we installed Debian Lenny on a server machine which was to be used as a Virtualization Server. Xen was then installed from the repository using the binaries. All was supposed to be okay. Xen was supposed to create the Xen kernel and update the GRUB menu.lst to include the Xen kernel. But, nope.. If something can go wrong, it will right? That’s what exactly happened. Following is the apt-get command I issued to install Xen.

apt-get install xen-hypervisor-3.2-1-amd64 xen-linux-system-2.6.26-2-xen-amd64 xen-utils-3.2-1 xen-utils-common

After the installation, there was no additional entry in the menu.lst that corresponded to the Xen kernel. I added the entry manually and booted from it. Whoa! Kernel Panic! Machine kept rebooting after showing the following error.

elf_init: not an ELF binary

Searching for through the forums and blogs was the next step, which suggested following possibilities.

Corrupt Xen Kernel or GRUB Entry
incorrect console entry on the GRUB
Incorrect or bad drivers for the SCSI drives

But, nope.. none of the above is possible. Then with the help of a colleague, it was clear that I was missing a package. So in a nutshell, if you are installing Xen on Debian Lenny this is the list of packages that you should use.

apt-get install xen-linux-system-2.6.26-2-xen-amd64 linux-modules-2.6-xen-amd64

Everything was cool after this. GRUB entries were updated. Booted in to the new kernel and voila! You have Xen!

10 Things to Remember When Installing Linux

Chamila | පිටස්තරයා — Sat, 07 Aug 2010 18:58:22 +0000

Not the usual bunch!

Always check twice before blindly pressing Return through the Key Board selection and the Country screens. Although I haven’t practically gone through one, one can’t simply risk having the key board respond in the most foolish manner ever.
If the installation seems to take a while, don’t leave the screen. There might be intermediate screens asking for stuff like, network mirrors etc. It is not pleasant to come back after half an hour to find out that the installation had been paused just for you to select the option “Yes” to install GRUB the minute you left.
Have separate /boot, /home and / (root) partitions if possible. This is common practice. Just to make sure that a 100Mb porn clip download would not keep the machine from booting.
Format the /boot partition as Ext2. Ext3 onwards introduce Journaling, and thus takes extra space to store the Journal. For the /boot partition, this feature is almost useless, as it is only needed to load the kernel and the ramdisk to the memory. Ext2 on a 200Mb partition will be more than enough.
Make sure to flag the boot partition as “Bootable” in the disk partitioning step. Although the Graphical Install option might just do this automatically, normal installations require you to specify the boot partition manually.
Skip the network information section if possible. You don’t want the installation to start downloading the latest packages and updates from the Internet, during the peak hours of the day.
Enter a strong root password in the installation. Chances are that after finishing the installation, you would most probably forget the root account (especially if you are a fan of sudo). And if you had entered an easy password, the people targeting the root account will have no hard time cracking it.
Remove any USB drives and portable storage devices before the installation starting step, in case you had plugged them into load drivers during the pre-installation steps. There is a good chance that the installer might use the portable drive to install the GRUB.
Learn Vi! The default text editor for the terminal in Linux is Vi and not Vim. Vi is designed considering only the QWERTY key board and not the arrow keys and the End, Home etc key set. Here is a good starting point.
Enable bash completion for your account. Bash Completion is the functionality which allows bash to complete the words on Tab press. This is particularly useful when using Apt (haven’t tried on Yum, but should work theoretically). This can be done by un-commenting the following lines in your $HOME/.bashrc file (or in some systems .bash_profile)

if [ -f /etc/bash_completion ] && ! shopt -oq posix; then . /etc/bash_completion fi