Posts Tagged ‘installation of RHEL/Centos’

Extracting/Recreating RHEL/Centos6 initrd.img and install.img

Tuesday, October 1st, 2013

A quick note about extracting and recreating RHEL6 or Centos6 (and their derivations) installation media components:



mv initrd.img /tmp/initrd.img.xz
cd /tmp
xz –format=lzma initrd.img.xz –decompress
mkdir initrd
cd initrd
cpio -ivdum < ../initrd.img

Archive (after you applied your changes):

cd /tmp/initrd
find . | cpio -o -H newc | xz -9 –format=lzma > ../new-initrd.img



mount -o loop install.img /mnt
mkdir /tmp/install.img.dir
cd /mnt ; tar cf – –one-file-system . | ( cd /tmp/install.img.dir ; tar xf – )
umount /mnt

Archive (after you applied your changes):

cd /tmp
mksquashfs install.img.dir/ install-new.img

Additional note for Anaconda installation parameters:

I did not test it, however there is a boot flag called stage2= which should lead to a new install.img file, other than the hardcoded one. I don’t if it will accept /images/install-new.img as its flag, but it can be a good start there.

One more thing:

Make sure that the vmlinuz and initrd used for any custom properties, in $CDROOT/isolinux do not exceed 8.3 format. Longer names didn’t work for me. I assume (without any further checks) that this is isolinux limitation.

Minimal Centos5 and SSH Server with X forwarding

Friday, October 10th, 2008

Installation of minimal selection of Centos 5 – only base, core and dialup selections, will leave a small-sized system, with the minimum required.

This is a good setup to start setting up a firewall, and it lets you add any required package later using ‘yum’.

This said, you cannot forward X over SSH at this state. A minimal setup is a minimal setup, after all. I was searching for the package required to allow X forwarding over SSH, and found it – xorg-x11-xauth

Install this one, and X will be forwarded over your SSH connection (you still need to connect with the ‘-X’ flag from the client).

RedHat / Centos Kickstart tweaks

Sunday, July 1st, 2007

Kickstart is a great method of hands-free installation of RHEL/Centos (and other derived systems). Its power is in its easy interface and rather powerful %post scripting directives. Its weakness is in its lack of flexibility where it comes to package selection and various custom actions.

On some cases, companies use web interface (usually home-made) which builds kickstart config files on-demand. On some cases, the administrator is required to build several kickstart config files for pre-anticipated setups.

I was looking for something which will give me the power to maintain a fixed configuration on one hand, and will allow me some tweaks and variants, when I want them. I could have used the %post scripting sections, but this gets quite complicated, especially when you want to add only one package (but with its dependencies), or you want to force full update of the system before it goes online, or even select its hostname, assuming it is not yet defined in the DNS.

I base my system on a simple DHCP/BootP + tftp server which answers to all bootp requests and offers a simple menu (just type a number and press on Enter). The original schema was quite simple: type 4 for Centos4.3, and then add -min if you wanted it to use a kickstart file with a minimum configuration. Then I wanted to add the option to update the system in an early stage, so I have added -update, which would have looked in the menu like “4-min-update” option. Quite readable, however, it generated lots of work when maintaining the pxelinux.cfg/default file and the ks themselves. Too many variations tend to require lots of care.

Adding parameters to the boot menu is possible, and would result in them existing in /proc/cmdline for later parsing.

I have decided to parse a set of predefined parameters supplied during boot time, and to change the kickstart config file according to them. It actually works quite well. This is a less-sophisticated and more of a stand-alone system compared to this system. Also, it doesn’t require me to alter the system’s boot process.

This is my ks.cfg file, which includes the flexibility additions:

# Kickstart file generated by Ez-Aton

nfs –server=install-server –dir=/mnt/samba/Centos
lang en_US.UTF-8
langsupport –default=en_US.UTF-8 en_US.UTF-8
keyboard us
network –device eth0 –bootproto dhcp
rootpw –iscrypted RpUKzjDc9k2gU
firewall –disabled
selinux –disabled
authconfig –enableshadow –enablemd5
timezone Asia/Jerusalem
bootloader –location=mbr


# By Ez-Aton
for i in `cat /proc/cmdline`; do
echo $i >> /tmp/vars.tmp
grep “=” /tmp/vars.tmp > /tmp/vars
. /tmp/vars
if [ ! -z “$update” ]; then
echo “yum update -y” >> $KS
if [ ! -z “$name” ]; then
value=”dhcp –hostname $name”
cat $KS | sed s/dhcp/”$value”/ > $KS.tmp
cat $KS.tmp > $KS
if [ ! -z “$pkg” ]; then
pkg_line=`grep -n ^%packages $KS | cut -f 1 -d :`
max_line=`wc -l $KS | awk ‘{print $1}’`
head -n $pkg_line $KS > $KS.tmp
for i in `echo $pkg | sed s/,/ /g`; do
echo $i >> $KS.tmp
let tail_line=$max_line-$pkg_line
tail -n $tail_line $KS >> $KS.tmp
cat $KS.tmp > $KS


So, as you can see, I take the following parameters:

update=yes (it can be update=anything)

name=hostname (in case it cannot be retrieved from the DHCP server)

pkg=pkg1,pkg2,{pkg3,…} (To add specific packages to the installation)

It was tested to work on Centos4.3 system, and will probably work on RHEL and Centos versions 4.x all along. I didn’t test it on RHEL5/Centos5 yet.

If you use the script, please leave my name and blog URL in it. Also, if you modify it for your needs, I would be glad to get back the modifications you have made, to include them.