Creating a USB install for Centos 6.4
The days of rotating disks for storing information and in particular for installing OSes are nearing their end. Why rely on something with rotating parts for storing data in the 21st century? Unfortunately, not every software vendor has caught up with this so in some cases special measures must be taken for installing an OS from a USB disk. One example of this is Centos/RHEL which does not come with a USB install by default. There is procedure from Red Hat that can be used, but that procedure is limited to starting an installation when you already have the installation media available somewhere (e.g. on a hard drive).
One common method to create such a USB install is to use the livecd-iso-to-disk script. Unfortunately that did not appear to work and I have tried it many times. After reading the interesting discussion on unix.stackexchange.com, I tried to give it another shot and this time it worked.
What I did was the following on a laptop running Centos 6.4:
- Insert the USB stick: Find out the device name (e.g. using dmesg). Make sure the stick is unmounted as it could be automounted.
- Partitioning: Make sure the disk is partitioned to contain one single primary partition (e.g. /dev/sdb1) using for example cfdisk. For now I will assume that /dev/sdb is the USB stick. Make sure to substitute this for the correct device in the next instructions.
- File system: Create an ext3 filesystem on /dev/sdb1
I did not try ext2 and ext4 but these could also work. You can also optionally do a
tune2fs -m0 /dev/sdb1
to increase the available space by removing reserved blocks for the kernel (these are not needed anyway).
- Install livecd tools: Install using yum:
yum install livecd-tools
- Transfer the ISO to the USB stick: Transfer disk 1 of the Centos 6.4 installation to the USB stick:
livecd-iso-to-disk CentOS-6.4-x86_64-bin-DVD1.iso /dev/sdb1
Note that it is important to specify /dev/sdb1 here and not /dev/sdb.
After this step, the USB stick can be tested locally using qemu-kvm.
To simply verify the the USB stick is found and the boot menu is recognized, bootup a virtual machine with only the USB disk:
/usr/libexec/qemu-kvm -hda /dev/sdb -m 256 -vga std
And use a VNC viewer (e.g. vncviewer from tigervnc) to view the VM. This should show a boot menu and should allow you to start the installation until the point that the installation procedure cannot continue anymore.
If you want to test a full installation, create a disk using logical volume management
lvcreate -L 10g -n bladibla vg_mylaptop
where vg_mylaptop is a volume group where you have at least 10GB of space left, and start qemu-kvm with the created logical volume as disk hdb and give it a bit more memory:
/usr/libexec/qemu-kvm -boot c -hda /dev/sdb -hdb /dev/vg_mylaptop/bladibla -m 2048 -vga std
After the install is completed, start the VM again without the USB stick
/usr/libexec/qemu-kvm -boot c -hda /dev/vg_mylaptop/bladibla -m 2048 -vga std
The VM should now start up successfully. The USB boot stick is also recognized by my laptop natively and I it looks like I can install a full OS also there (at least the upgrade, which did nothing of course in my case, worked completely).
Disclaimer: As mentioned in the discussion at the link above, the whole procedure might give different results based on the USB stick you might use. I tested this procedure on a Dell Latitude M4700 laptop using a Kingston GT160 8GB memory stick.